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ELEMENTS 


OF 


PHYSIOLOGY 


v        AND 


HYGIENE. 


BY 
R.     T.    BROWN,    M.D., 

CHEMIST  IN  CHIEF.  DEPARTMENT  OP  AGRICULTURE,  WASHINGTON,  D.  C. 


WILSON,  HINKLE   &   CO., 

137   WALNUT   STREET,  28   BOND    STREET, 

CINCINNATI.  NEW   YORK. 


- 

G 


Entered  according  to  Act  of  Congress,  in  the  year  1872,  by 

WILSON,  H1NKLE   &  CO., 
In  the  Office  of  the  Librarian  of  Congress,  at  Washington,  D.  C. 

ELECTROTYPE!)  AT   THE   FRANKLIN  TYPE  FOUNDRY,  CINCINNATI. 

EDUCATION! 


PREFACE. 


THE  following  lessons  in  Physiology  and  Hygiene  were  prepared 
in  response  to  a  resolution  of  the  INDIANA  STATE  TEACHERS'  ASSO- 
CIATION. They  were  designed  originally  to  meet  a  demand  in  that 
State,  where  the  law  introduces  these  branches  of  study  into  common 
schools.  In  the  execution  of  this  design  the  author  has  endeavored  to 
prepare  a  work  adapted  to  the  wants  of  families  and  the  general 
reader. 

Physiology  and  Hygiene  having  been  but  recently  introduced  into 
the  common  literature  of  the  country,  parents,  generally,  have  only  a 
limited  knowledge  of  a  subject  which  stands  in  most  intimate  connec- 
tion with  the  well-being  of  those  intrusted  to  their  care.  To  such 
persons  the  following  lessons  present  the  elementary  principles  of 
human  physiology,  and  the  laws  of  health,  deduced  therefrom,  di- 
vested, as  far  as  possible,  of  the  technical  dress  which  too  often 
places  these  subjects  beyond  the  comprehension  of  common  readers. 

It  is  of  the  first  importance  to  those  who  have  the  care  of  chil- 
dren, whether  in  the  family  or  the  school,  that  they  make  themselves 
familiar  with  the  laws  of  health,  in  order  that  they  may  establish,  in 
early  years,  habits  of  correct  living  in  those  under  their  charge.  The 
value  and  duration  of  human  life  are  more  intimately  connected  with 
the  establishment  of  such  habits  than  is  generally  admitted.  If  wrong 
ones  are  formed  in  childhood,  the  power  to  correct  them  in  maturer 
years  is  often  wanting ;  and  even  if  efforts  in  that  direction  prove 
successful,  still  the  evil  consequences  remain. 

It  must  be  remembered  that  habits  injurious  to  health,  when  estab- 
lished in  youth,  while  the  vital  organs  are  in  a  state  of  development, 
leave  an  impression  of  a  deeper  and  more  permanent  character  than 
similar  habits  formed  in  after  life.  To  prevent  these  evils  rather  than 
to  reform  them  is  the  true  philosophy. 

To  this  end  the  author  invokes  the  aid  of  parents  and  teachers,  and 
as  his  contribution  to  what  he  conceives  to  be  the  best  method  of 
instruction,  presents  these  lessons,  trusting  they  will  tend  toward 
awakening  an  interest  in  subjects  of  vital  importance  to  all. 

543511  («i> 


iv  PKEFACE. 

Many  text-books  on  the  science  of  Physiology  and  Hygiene  have 
l)cen  presented  to  the  schools  and  colleges  of  this  country  during  the 
past  few  years.  These  are  chiefly  abridgments  of  the  larger  works 
used  in  medical  colleges ;  and  as  physiology  is  taught  in  those  schools 
with  a  direct  reference  to  the  cure  of  disease,  these  books  retain  more 
or  less  of  this  character.  But  the  study  of  physiology  in  other  than 
medical  schools  should  have  direct  reference  to  the  preservation  of  health, 
rather  than  to  the  cure  of  disease.  It  has  been  the  leading  purpose  of 
the  author  to  make  HYGIENE  the  prominent  feature  of  this  book,  and 
all  other  studies  introduced  subordinate  to  it. 

To  the  scientific  reader  the  author  wishes  to  say,  that  while  he  has 
aimed  to  present  his  subject  in  a  popular  form,  and  avoid  the  discus- 
sion of  many  purely  scientific  questions  which  might  have  been  intro- 
duced, it  has,  at  the  same  time,  been  his  purpose  to  treat  it  in  the  light 
of  the  latest  discoveries. 

In  the  use  of  such  terms  as  vital  force,  etc.,  the  author  does  not 
intend  to  commit  himself  to  any  particular  theory  of  life,  but  merely 
uses  such  phrases  as  siyns  of  the  unknown. 


HINTS    TO   TEACHERS. 

This  book  is  divided  into  fifty  lessons,  with  the  intention  of  adapt- 
ing it  to  the  common  division  of  the  school  year  into  terms  of  about 
twelve  weeks  each.  If  five  lessons  are  recited  each  week,  the  work  can 
be  completed  in  a  term,  and  ten  recitations  be  left  for  review. 

If  it  is  desirable  to  give  more  time  to  the  study,  the  lessons  may 
be  divided  and  the  work  distributed  over  two  terms,  devoting  the  first 
to  Physiology  and  the  second  to  Hygiene. 

For  the  purpose  of  easy  reference,  the  work  is  divided  into  sections 
and  each  one  is  numbered.  To  adapt  it  to  the  method  of  teaching  by 
topics,  each  section  is  introduced  by  a  head-line  in  full-faced  type, 
embracing  the  leading  subject. 

Brief  recapitulations  are  appended  to  the  lessons,  for  the  assistance 
alike  of  teachers  and  pupils  in  the  work  of  reviewing. 

Much  of  the  work  of  teaching  this  science  should  be  done  by  lec- 
tures, or  by  familiar  conversations  between  pupils  and  the  teacher; 
and  in  the  arrangement  of  the  matter  of  these  pages  this  feature  has 
been  kept  constantly  in  view. 


CONTENTS. 


Page 

LESSON  I. — Introduction       .        .        .      ^  •    .  •  ,  •  vv »        •  7 

LESSON  II. — Definitions  and  Classifications          <        ,-:     .        .  13 
LESSON  III. — Nutrition        .        .         ......    «„    ,»        •        .19 

LESSON  IV. — Digestion 24 

LESSON  V. — Circulation 31 

LESSON  VI.— Circulation  —  Continued 36 

LESSON  VII. — Kespiration    . 41 

LESSON  VIII.— Purification  of  the  Blood 46 

LESSON  IX. — Growth  and  Repair 52 

LESSON  X. — System  of  Voluntary  Motion 58 

LESSON  XI. — Skeleton 63 

LESSON  XII.— Muscles          . 72 

LESSON  XIII. — Muscular  Motion  —  Voice 78 

LESSON  XIV.— Nervous  System 83 

LESSON  XV. — Nervous  System  —  Continued        ....  90 

LESSON  XVI. — Sensation 96 

LESSON  XVII.— Organs  of  Special  Sense      .         .        .        .        .  101 

LESSON  XVIII.— Hearing 106 

LESSON  XIX.— The  Eye Ill 

LESSON  XX.— Vision .117 

LESSON  XXI. — Vision  —  Continued 123 

LESSON  XXII.— Motor  Functions 128 

LESSON  XXIII.— Nervous  Functions 133 

LESSON  XXTV.— Mental  Functions 138 

(v) 


u 
vi  CONTENTS. 

Page 

LESSON  XXV.— Sleep 143 

LESSON  XXVI.— Health 149 

LESSON  XXVII.— Food  and  Drink 154 

LESSON  XXVIIL— Classification  of  Food 160 

LESSON  XXIX.— Quality  of  Food 165 

LESSON  XXX.— Quality  of  Food  — Continued     .        .         .        .170 
LESSON  XXXI— Mode  of  Preparing  Food  .        .        .        .175 

LESSON  XXXII —Auxiliary  Food 180 

LESSON  XXXIII.— Quantity  of  Food 185 

LESSON  XXXIV —Time  of  Taking  Food 190 

LESSON  XXXV— Condition  of  the  System 196 

LESSON  XXXVI.— Circulation 201 

LESSON  XXXVIL— Breathing 206 

LESSON  XXXVIII.— Pure  Air     .        .        .   '     .        .        .        .211 

LESSON  XXXIX.— Animal  Heat 216 

LESSON  XL.— Bathing  — Clothing 222 

LESSON  XLI. — Hygiene  of  Bones         ......    227 

LESSON  XLII. — Muscular  Exercise       .        .        .        .        .        .     232 

LESSON  XLIII.— Exercise  and  Kest 237 

LESSON  XLIV.— Brain  Rest 242 

LESSON  XLV.— Brain  Poisons 248 

LESSON  XLVL— Brain  Poisons  —  Continued        .        .        .        .253 
LESSON  XLVII. — Brain  Poisons  —  Continued      ....     258 

LESSON  XLVII  I.— Tobacco 263 

LESSON  XLIX—  Brain  Exercise  and  Best  .        .        .  .268 

LESSON  L. — Accidents  and  Diseases  ,    273 


;    // 


PART   I. 

PHYSIOLOGY. 


LESSON    I. 

INTRODUCTION. 

1.  Classification  of  Bodies.  —  The    material   things 
that  are  around  us  in  this  world  may  be  divided  into 
two  classes  —  those  which  were   formed  by  the  coming 
together  of  particles  of  matter  under   the   simple  laws 
of  attraction,   and   those   which    have   grown   to   their 
present  size  and  shape  under  the  influence  of  that  force 
which  we  call  Life. 

Chemistry  teaches  us  how  the  first  class  of  bodies  are 
formed;  and  Mechanical  Philosophy  tells  how  they  op- 
erate on  each  other,  and  defines  the  laws  governing 
their  movements. 

Physiology  instructs  us  in  the  mysteries  of  life-formed 
bodies,  as  far  as  these  may  be  known.  It  may  therefore 
very  properly  be  called  The  Science  of  Life. 

2.  Organic  Bodies. — The  difference  in  the  growth  of 
a  living  body,  and  the  increase  in  size  of  a  body  which 

(7) 


PHYSIOLOGY. 

alive,  have  given  rise  to  the  following  method  of 
g;  and  'learning  bodies,  which  is  now  very  gen- 
erally'received. 

A  plant  takes  up  the  matter  intended  for  its  growth 
by  means  of  vessels,  or  open  mouths  provided  for  that 
purpose,  either  in  its  roots  or  leaves.  In  these  vessels, 
this  matter  undergoes  the  changes  that  fit  it  to  become 
a  part  of  the  living  plant,  and  by  them  it  is  carried  to 
its  proper  place  and  built  into  the  structure  of  the  body. 
These  instruments  by  which  the  food  is  absorbed,  pre- 
pared, and  deposited  are  called  Organs,  and  the  body  thus 
formed  is  an  Organic  body. 

3.  Inorganic  Bodies. — A  stone  placed  in  water  which 
holds  lime  dissolved  in  it,  as  the  waters  of  many  springs 
do,  will  increase  in  size  by  the  addition  of  particles  of 
lime  to  its  outer  surface;   but  in  making  this  apparent 
growth,  no  vessels  are  employed  to  carry  the  lime  to  its 
place,  and  no  instruments  are  used  to  change  either  its 
form  or  place. 

A  rock  thus  formed  is,  therefore,  an  Inorganic  body. 
These  two  classes  embrace  all  bodies  of  matter  on  the 
earth.  To  the  inorganic  group  belongs  the  great  mass 
of  material  of  which  the  globe  is  formed,  such  as  rocks, 
earths,  metals,  etc. 

4.  Character  of  Organic  Bodies. — The  organic  world 
is  made  up  of  but  a  few  simple  elements;  but  the  bodies 
are  very  complex,  both  in  their  form  and  composition. 
They  are,  moreover,  much  less  fixed  and  permanent  in 
their  character  than  inorganic  bodies. 

While  an  organic  body  lives,  it  is  constantly  under- 
going change  by  growth,  or  by  decay  and  repair;  and  as 
soon  as  it  ceases  to  live,  a  tendency  to  decomposition 


T 

INTRODUCTION.  9 

ensues,  and  the  body — it  may  be  slowly,  '-but  ver^ 
surely  —  returns  its  matter  to  the  •  inojrjgaaicj  worlds  fjroiri 
which  it  was  taken. 

5.  Division  of  the  Organic  World.— Organic  bodies 
are  of  two  kinds  —  Vegetable  and  Animal.     These  are  alike 
formed   under   the   influence   of   the   life-force,  and  by 
means  of  organs,  yet  they  differ  from  each  other  in  their 
general  characteristics.    This  difference  is  most  apparent 
in  the  higher  and  more  perfect  forms  of  both  classes; 
but  as  we  descend  in  the  scale  of  life,  these  two  grand 
divisions  approach  so  near  to  each  other  that  it  is  al- 
most impossible  to  define  the  line  separating  them. 

The  distinction  which  most  persons  would  first  ob- 
serve is  that  plants  are  fixed  to  one  spot,  while  animals 
enjoy  the  power  of  changing  their  place.  While  this  is 
generally  true,  it  is  not  so  universally.  The  sponges 
and  corals  of  the  ocean  are  as  firmly  fixed  to  one  spot 
as  the  trees  of  the  forest. 

6.  Animal  Characteristics.  —  Animals  are  described 
as  having   a   nutritive   cavity — a  stomach  into  wrhich 
food  is  taken,  and  where  it  is  prepared  to  be  used  for 
the  growth  and  repair  of  the  living  body.     In  the  veg- 
etable, the  food  is  absorbed  either  by  the  roots  or  leaves, 
and  it  undergoes  no  previous  preparation  to  fit  it  to  be 
thus  absorbed. 

This  distinction  applies -only  to  those  animals  whose 
structure  conforms  to  the  regular  types  of  animal  life. 
No  internal  cavity  can  be  found  in  many  of  the  lower 
and  irregular  forms  of  animal  life.  Plants  live  on  inor- 
ganic food;  animals  digest  and  assimilate  only  that 
which  has  been  organized.  This,  in  the  strict  meaning 
of  its  terms,  is  true ;  yet  it  is  evident  that  animals  ap- 


10  PHYSIOLOGY. 


e'r;  alid.  various  mineral  substances,  though 
tpr€tbjab}y^witJioiiit.'tansv;rTligestive  change. 

7.  Nervous  System  —  the  true  distinction.  —  The  real 
difference  between  animal  and  vegetable  life  consists  in 
the  possession  of  a  Nervous  System,  and  the  manifestation 
of  its  functions,  in  a  greater  or  less  degree,  by  all  ani- 
mals.    These  are  the  powers  of   sensation,  perception, 
and  voluntary  motion.     In  the  lower  forms  of  animal 
life,  the  nervous  system  is  very  imperfect  ;  yet  the  un- 
mistakable evidence  of  feeling,  and  the  power  to  move 
at  the  command  of  the  will,  though  the  motion  may  be 
to  a  very  limited  extent,  demonstrate  its  existence,  even 
though  the  microscope  may  not  reveal  the  nervous  cen- 
ters. 

8.  Animal  Sub-kingdoms.  —  While  all  animals  have 
an  apparatus  of  voluntary  motion,  and  organs  for  receiv- 
ing,  transmitting,   and  perceiving   sensations,   yet   the 
degree  of  perfection  in  which  these  animal  powers  are 
possessed,  is  so  widely  different  as  to  give  room  for  the 
division  of  the  animal  kingdom  into  several  sub-king- 
doms, each  distinguished  by  some  common  element  of 
form,  which  constitutes  what  is  called  the  type  of  the 
sub-kingdom. 

At  the  base  of  the  pyramid  of  animal  life  lies  a  group 
of  forms,  exceeding  in  numbers,  perhaps,  all  other  classes 
of  animals,  yet  so  minute  as  to  be  seldom  visible  to  the 
naked  eye,  and  are  therefore  studied  chiefly  by  aid  of 
the  microscope.  They  are  called  Protozoans,  a  word 
which  means  first  life.  These  are  exceedingly  simple, 
yet  they  present  endless  varieties  of  form.  As  they 
do  not  conform  to  any  special  type,  they  are  very 
difficult  of  classification. 


INTRODUCTION. 


11 


Rising  above  these,  we  have  four  well  defined  types 
of  life,  which  we  enumerate  in  the  ascending  order. 


FIG.  1.— STAB-FISH. 


1st.  Radiate  Animals,  or  those  with  arms  or  feelers  ex- 
tending in  every  direction,  like  rays,  from  the  mouth, 
which  is  simply  an  opening  into  the  central,  digestive 
cavity. 


FIG.  2.— SNAIL. 


2d.  Mollmks,   or   soft-bodied   animals   without    limbs; 
such  as  snails,  oysters,  clams,  etc. 

FIG.  3.— DRAGON-FLY. 


3d.  Articulates,  or  animals  whose  bodies  are  made  of 


12 


PHYSIOLOGY. 


rings  joined  together,  as  in  the  lobster,  craw-fish,  and  in- 
sects generally. 

4th.  Vertebrates.  Animals  with  a  bony  col- 
umn extending  the  whole  length  of  the  body, 
and  inclosing  a  nervous  cord  with  a  more  or 
less  perfectly  developed  brain  at  its  forward 
termination. 

9.  Classification  of  Vertebrate  Animals. — 

Of  this  last  and  most  perfect  type  of  animal 
life  we  enumerate,  in  the  ascending  order, 
four  grand  sub-divisions,  distinguished  from 
each  other  by  very  well  marked  natural  pecu- 
liarities. These  are : 

1st.  Fishes.  Inhabiting  the  water,  and 
breathing  by  means  of  gills.  They  are  usu- 
ally covered  with,  scales. 

2d.  Reptiles.  Breathing  air  with  very  imperfectly 
formed  lungs,  and  generally  having  the  body  naked. 
Fishes  and  reptiles  are  cold-blooded  animals,  the  tem- 
perature of  the  body  being  nearly  that  of  the  water  or 
air  in  Avhich  they  live. 

3d.  Birds.  Warm-blooded  animals,  covered  with  feath- 
ers, and  provided  with  wings  for  flying.  With  the  ex- 
ception of  a  few  reptiles,  these  three  classes  produce  their 
young  from  eggs. 

4th.  Mammals.  Animals  which  suckle  their  young. 
Their  bodies  are  usually  covered  with  hair. 

Recapitulation. 

An  Organ  is  any  thing  used  as  an  instrument  to  accomplish  a 
purpose. 

That  which  is  done  by  an  organ  is  called  its  function.  Exam- 
ple :  The  teeth  are  organs ;  chewing  food  is  their  function. 


DEFINITIONS  AND  CLASSIFICATIONS.  13 

A  body  which  grows  and  maintains  its  repairs,  by  means  of  the 
life  force  exerted  through  organs,  is  called  an  Organic  body,  and 
the  laws  regulating  the  proper  action  of  these  organs  constitute 
its  Physiology. 


LESSON   II. 

DEFINITIONS   AND   CLASSIFICATIONS. 

10.  Range  of  Physiological  Science. — Anatomy  de- 
scribes the  different  parts  or  organs  of  an  organic  body, 
while  Physiology  teaches  the  use  of   each   organ,  and 
describes  its  mode  of  action.     As  we  have  vegetable  and 
animal  bodies,  and  both  are  organic, -so  we  have  vegeta- 
ble anatomy  and  physiology,  and  animal  anatomy  and 
physiology.     The  first  of  these  belongs  properly  to  the 
science  of  Botany;  the  last  is  very  appropriately  divided 
into   two  sections:  Comparative  Anatomy  and  Physiol- 
ogy, and  Human  Anatomy  and  Physiology. 

The  first  of  these  sections  is  devoted  to  the  peculiar 
forms  of  the  several  organs  and  their  functions  in  the 
lower  animals,  as  compared  with  the  corresponding  or- 
gans and  functions  in  the  human  body. 

11.  Limits  of  the  present  study.— In  the  following 
pages  we  propose  to  confine  the  discussion  to  the  subject 
of  Human  Anatomy  and  Physiology,  chiefly.     Xo  more 
of  descriptive  anatomy  will  be  given  than  will  enable 
the  reader  or  student  to  understand  the  functions  of  the 
several  organs  described,  and  to  treat  these  organs  and 
functions  so  as  to  maintain,  in  the  most  perfect  manner, 
their    natural   condition    and   proper   action.     This    is 
health. 


14  PHYSIOLOGY. 

What  Life  is,  we  may  not  know;  but  what  it  does, 
and  the  laws  by  which  it  acts,  are  legitimate  subjects 
of  knowledge,  as  clearly  within  our  reach  as  any  other 
science. 

12.  Animal  and  Vegetable  Nutrition  —  the  differ- 
ence.— Though  the  laws  of  animal  life,  in  their  leading 
and  essential  features,  are  the  same  in  the  lower  ani- 
mals as  in  man,  yet  in  many  of  the  details,  both  in  the 
form  of  special  organs,  and  the  manner  in  which  these 
perform  their  functions,  there  is  a  wide  difference  be- 
tween the  merely  animal  and  the  human. 

All  living  bodies  grow  by  absorbing  substances  unlike 
that  of  their  own  body,  and  by  so  changing  it  as  to 
convert  it  into  a  substance  exactly  like  that  of  their 
own  organs.  This  is  nutrition,  and  is  a  function  com- 
mon to  all  organic  bodies.  In  vegetables,  the  matter 
thus  appropriated  remains  a  part  of  the  body  till  the 
whole  structure  or  organ  dies,  and  by  decay  returns  to 
the  inorganic  world. 

In  animals  the  matter  furnished  by  nutrition,  after 
it  has  served  its  purpose  for  a  time,  is  removed,  particle 
by  particle,  new  matter  being  prepared  and  furnished 
by  digestion  to  supply  the  place  of  the  worn-out  par- 
ticles removed. 

13.  Animal  Functions. — The  work  of  repair  is  a  feat- 
ure which  characterizes   animal  life,  and  is  common  to 
all  its  forms;  indeed,  this  change  of  matter  is  not  only 
common  to  all  animals,  but  is  essential  to  the  mainte- 
nance of  active  life  in  them. 

The  manner  in  which  motion  is  performed,  is  the 
same  in  man  as  in  all  other  animals,  however  widely 
they  may  differ  from  the  human  form,  or  from  each 


DEFINITIONS  AND  CLASSIFICATIONS.  15 

other.  The  breathing  apparatus  differs  in  many  par- 
ticulars in  different  animals;  but  to  breath  air,  either 
by  itself  or  in  mixture  with  water,  is  a  condition  of 
active  life  from  which  no  animal  can  escape. 

14.  Relation  o£  Man  to  the  lower  Animals.  —  In  all 

these  respects  man  is  an  animal,  but  in  other  respects  he 
is  more  than  an  animal.  He  has  many  characteristics 
that  are  purely  human.  In  the  frame-work  of  his  body, 
man  is  constructed  for  an  upright  position;  while  in  all 
other  animals  the  natural  position  is  that  in  which  the 
spinal  column,  or  backbone,  is  horizontal,  or  nearly  so. 
Even  the  monkey  when  taught  to  stand  erect  does  so 
with  evident  difficulty,  and  all  his  movements  show  his 
position  to  be  a  constrained  one. 

The  configuration  of  the  human  face  differs  in  many 
features  from  that  of  any  other  animal.  For  example: 
the  lower  jaw  of  all  the  inferior  animals  drops  back  im- 
mediately from  the  front  teeth,  while  that  of  man  pro- 
jects forward,  forming  a  chin.  Certain  very  expressive 
functions  or  actions  are  peculiar  to  man,  such  as  the 
power  to  shed  tears,  to  laugh,  to  communicate  his 
thoughts  by  articulate  language,  etc. 

15.  Classification   of  Man.  —  Naturalists   concur    in 
placing  man  at  the  head  of  the  animal  creation.     They 
place  him  in  an  order  distinct  and  separate  from  all 
other  animals;   and  recognizing  the  fact  that  he  alone 
has   two   hands,  they  name   that  order  BIMAXA;    while 
monkeys  are  regarded  as  four-handed  animals,  and  there- 
fore as  constituting  the  order  Quadrumana. 

If  we  study  carefully  the  structure  of  that  wonderful 
organ — the  human  hand,  and  observe  closely  its  marvel- 
ous endowments   and  capabilities,  we  shall  hardly  be 
B.  P.— 2. 


16  PHYSIOLOGY. 

willing  to  say  that  a  baboon  is  furnished  with  four  such 
Drgans !     The  feet  of  a  monkey  are  not  real  hands. 

16.  Mental  and  Moral  Distinctions. — But  it  is  chiefly 
in  the  perfection  of  his  nervous  system,  and  his  superior 
mental  endowments,  that  man  rises  above  the  mere  ani- 
mals that  surround  him,  and  stands  alone  in  his  endow- 
ments and  capacities.  The  inferior  animals  certainly 
think  and  make  inferences  with  regard  to  matters  of 
their  own  personal  experience  —  and  so  far  they  may  be 
said  to  reason ;  but  they  are  wholly  incapable  of  reason- 
ing on  the  abstract  qualities  of  things,  or  of  deducing 
general  truths  from  special  manifestations. 

The  moral  sense  —  the  abstract  idea  of  right  and 
wrong — is  exclusively  a  human  faculty,  and  belongs  to 
man's  spiritual  nature.  This  is  not  merely  a  higher 
degree  of  the  reasoning  power  of  brutes,  but  a  different 
kind  of  reasoning. 

II.  Abstract  Thought  —  a  human  attribute.  —  It  is 

to  this  power  of  abstract  thought  that  man  is  indebted 
for  his  ability  to  contrive  and  construct  machines  to  re- 
lieve his  hands  from  the  drudgery  of  manual  toil;  by 
this  he  discovers  and  applies  natural  laws,  invents  sci- 
ence, and  perfects  literature.  While  he  is  an  animal  — 
a  very  perfect  animal  in  all  his  physical  organs  and 
faculties  —  he  is  something  more  than  an  animal  in 
this. 

This  superior  mental  endowment  should  be  made  the 
basis  of  his  classification;  and  as  only  organic  life  is 
displayed  in  the  vegetable  world,  and  this,  with  the 
animal-powers  of  sensation  and  volition  superadded,  is 
embodied  in  the  animal  kingdom,  so  both  these,  with  the 
powers  of  abstract  reason,  moral  sensibility,  and  the 


DEFINITIONS  AND  CLASSIFICATIONS.  17 

devotional  attributes  of  his  nature  mark  him  as  belong- 
ing to  a  grade  of  life  as  much  above  the  mere  animal 
as  the  animal  is  above  the  vegetable. 

18.  Form  of  Matter  composing  the  Organs  of  the 
Body.  —  But  our  present  task  is  to  study  man  in  the 
structure  of  that  body  which  he  has  in  common  with 
other  living  organisms,  and  in  the  laws  by  which  the 
various   movements   of  that  complicated  machine   are 
governed.     Before  entering  on  the  study  of  this  subject 
in  detail,  a  few  general   statements  and  explanations 
may  be  of  use  in  its  introduction. 

The  human  body  is  composed  of  solids,  semi-solids, 
and  fluids.  These  arc  constantly  changing  while  the 
body  lives.  The  semi-solid  flesh,  as  well  as  the  firm, 
compact  bone,  was  once  fluid  in  the  form  of  blood;  and, 
in  due  time,  particle  by  particle,  they  will  be  dissolved, 
and  becoming  fluid  again,  will  be  carried  away. 

19.  Tissues  —  their    several   offices.  —  The    several 
parts  of  the  body  differ  from  each  other  in  the  character 
of  their  structure  as  well  as  in  the  substances  out  of 
which  they  are  formed.      These  different  structures  are 
called  Tissues.     So  we  have  the  bony  or  osseous  tissue  in 
the  bones  which  form  the  solid  frame-work  of  the  body; 
the  fibrous  tissue  in  the  muscles  which  move  these  bones; 
the  membranous  tissue  in  the  delicate  skin  or  membrane 
which  covers  each  organ,  and  lines  every  cavity  of  the 
body;   the  areolar  or  cellular  tissue  which  fills  all  the 
spaces   between  the  organs,  and   gives    roundness   and 
symmetry  to    the   outlines   of   the  body;    the   nervous 
tissue,  that  delicate  structure  seen  in  the  substance  of 
the  brain,  and  in  thoso  white  cords — the  nerves — which 
extend  from  it  to  all  parts  of  the  body. 


18  PHYSIOLOGY. 

20.  The  three  Systems. — The  living  human  body, 
though  evidently  a  unit;  may  yet  be  regarded,  in  its 
varied  and  complicated  actions,  as  three  systems  acting 
in  concert  with  each  other.  These  are : 

1st.  The  System  of  Nutrition,  consisting  of  the  apparatus 
of  Digestion,  of  Circulation,  and  of  Respiration. 

2d.  The  System  of  Voluntary  Motion,  consisting  of  a  bony 
skeleton  with  its  joints  and  ligaments,  and  a  muscular 
apparatus  so  constructed  and  arranged  as  to  produce  a 
great  variety  of  motions. 

3d.  The  System  of  Nervous  Sensibility  and  Motor  Force. 
This  consists  of  the  brain  and  spinal  cord,  with  numer- 
ous nerves  branching  and  ramifying  through  every  tissue 
of  the  body.  These  several  systems  we  shall  proceed  to 
consider  in  order. 

Recapitulation,, 

Comparative  Physiology  likens  the  organs  of  inferior  animals 
to  those  of  man.  This  book  treats  of  organs  and  their  functions 
chiefly  with  reference  to  the  preservation  of  health. 

Vegetables  acquire  matter  for  growth  which  becomes  perma- 
nent. Worn-out  animal  matter  is  replaced  by  new.  Man  is 
more  than  an  animal  in  figure,  face,  and  functions.  Man  forms 
the  order  Bimana;  is  distinguished  by  mental  capacity,  moral 
nature,  and  capability  for  abstract  thought. 

The  body  is  composed  of  solids,  semi-solids,  and  fluids.  Tis- 
sues are  osseous,  fibrous,  membranous,  areolar,  and  nervous. 
The  three  systems  in  one  body. 


NUTRITION.  19 

LESSON    III. 

NUTRITION. 

21.  Classification  of  Food. — The  process  of  supplying 
material  fitted  for  the  growth  and  repair  of  the  living 
body  is  properly  nutrition;  hut  as  the  maintenance  of 
animal  heat  is  intimately  connected  with  this  matter 
of  nutrition,  we  shall  consider  them  together,  as  parts 
of  one  process. 

The  crude  material  of  nutrition  is  known  by  the  gen- 
eral name  of  Food.  This  consists,  however,  of  two  classes 
of  substances  —  that  which  supplies  the  material  for  the 
growth,  and  also  to  repair  the  wastes  of  the  several 
tissues  of  the  body;  and  that  which,  being  consumed, 
constantly  gives  off  heat  to  maintain  the  uniform  tem- 
perature of  the  body. 

The  first  class,  from  the  close  resemblance,  in  chem- 
ical composition,  which  all  the  articles  of  it  bear  to  al- 
bumen (which  is  the  substance  of  the  white  of  eggs),  is 
called  albuminate  food,  and  the  latter  class  is  known 
as  carbonaceous  food. 

22.  The  Mouth  — its  functions.— The  first  act  of  nu- 
trition is  performed  in  the  mouth,  and  is  called  mastica- 
tion.    It  consists  of  crushing  and  grinding  the  food,  thus 
reducing  it  to  a  state  of  fine  division,  and  at  the  same 
time  moistening  it  with  a  -fluid  furnished  for  the  pur- 
pose called  saliva.    The  mouth,  where  this  work  is  done, 
is  lined  with  a  smooth  covering  always  kept  moist,  when 
in    a   healthy  condition,   by  a  glairy  fluid  known  as 
mucus,  and  hence   this   surface   is   named  the   mucous 
membrane. 


20 


PHYSIOLOGY. 


This  kind  of  a  membrane  lines  all  cavities  of  the  body 
which  communicate  in  any  way  with  the  air  •  while  all 
the  closed  cavities,  and  the  organs  contained  in  them, 
are  lined  and  covered  with  a  dense,  smooth,  shining 
coat,  called  a  serous  membrane. 

FIG.  5.— PERMANENT  TEETH. 


a.  Jucisors.    b.  Cuspids,    c.  Bi-cuspids.    d.  Molars,    e.  Wisdom-teeth. 


23.  Mastication— Classification  of  the  Teeth.— The 

grinding  of  the  food  is  performed  by  the  Teeth.  These 
are  composed  of  a  very  hard,  compact,  bony  substance, 
covered  with  a  material  still  harder  called  enamel. 
There  are  two  sets  of  teeth.  The  first,  or  temporary 
teeth,  consist  of  ten  in  each  jaw.  They  appear  in  in- 
fancy, and  continue  six  or  eight  years,  when  they  become 
loose  and  are  crowded  out  by  the  permanent  teeth.  Of 
these  there  are  sixteen  in  each  jaw,  or  thirty-two  in  all. 
The  teeth  are  divided  into  four  classes,  as  follows: 
The  four  front  teeth  in  each  jaw  are  called  incisors,  or 
cutting-teeth;  the  next  tooth  on  each  side  of  these  is 
the  cuspid,  or  canine-tooth ;  next  follow  two  bi-cuspids 


NUTRITION.  21 

on  each  side;  and,  lastly,  three  molars,  or  grinding- 
teeth,  in  each  jaw.  The  last  of  these,  on  each  side,  is 
called  the  wisdom-tooth,  because  it  does  not  appear 
until  a  person  is  twenty,  and  sometimes  twenty-five 
years  old. 

FIG.  6.— SALIVARY  GLANDS. 


a.  Parotid  gland.        6.  Parotid  duct.        c.  Sublingnal  gland. 
d.  Submaxillary  gland.          e.  Submaxillary  duct. 

2±.  Salivary  Glands.  — The  saliva,  with  which  the 
food  is  moistened  in  mastication,  is  furnished  by  a  set 
of  bodies  called  Salivary  elands,  whose  office  it  is  to 
separate  this  fluid  from  the  blood.  All  the  special  fluids 
of  the  body  are  produced  in  a  similar  manner,  so  that 
the  glands  form  an  important  group  in  the  vital  econ- 
omy. Their  action  is  called  secretion. 

The  salivary  glands  are  three  in  number  on  each 
side.  The  largest  of  these,  called  the  Parotid  gland,  is 


22  PHYSIOLOGY. 

situated  behind  the  angle  of  the  lower  jaw,  and  forward 
of  the  external  ear.  It  sends  its  saliva  into  the  mouth 
through  a  tube  or  duct  which  opens  opposite  the  second 
molar  tooth,  in  the  upper  jaw. 

The  second  pair,  the  Submaxillary  glands,  are  located 
on  the  inner  side  of  the  lower  jaw,  a  little  forward  of 
the  angle,  on  each  side.  The  Sublingual  glands  are 
placed  beneath  th6  mucous  membrane,  forming  the 
floor  of  the  mouth,  on  each  side,  near  the  base  of  the 
tongue. 

25.  Saliva  —  its  use.  —  The  movement  of  the  jaw  in 
the  act  of  chewing  excites  these  glands  to  activity,  and 
they  pour  out  a  bland  fluid,  nearly  transparent  and  a 
little  heavier  than  water.    This  saliva,  when  mixed  with 
food  of  the  nature  of  starch,  has  the  power  of  slowly  con- 
verting it  into  sugar.      Now   starch,  which    forms    the 
greater  part  of  bread,  potatoes,  and  such  articles  of  food, 
will  not  dissolve    in  water;    but  when  converted  into 
sugar,  it  is  very  readily  dissolved.     It  will  be  observed, 
then,  that  the  saliva  is  not  intended  merely  to  moisten 
the  food  that  it  may  be  swallowed  easily.     Tea,  cohee, 
water,  or  milk  may  be  used  for  that  purpose,  but  neither 
of  these  can  be  substituted  for  saliva  without  injuring 
digestion,  for  neither  of  them  can  change  starch  into 
sugar,  or  render  it  soluble  in  water. 

26.  Pharynx — its  office. — In  the  act  of  chewing,  the 
tongue  is  used  to  keep  the  food  pressed  between  the 
teeth;    and  finally,  when  it  is  thoroughly  reduced  to  a 
pulp,  the  tongue  rolls  it  into  a  little  ball,  and  carries  it 
along  its  upper  surface  to  the  back  part  of  the  mouth, 
passes  it  between  the  pillars  of  the  fauces,  and  under  the 
hanging  palate.     These  organs  form  a  kind  of  gate-way 


NUTRITION. 


23 


FIG.  7. 


from  the  mouth  into  the  Pharynx.  This  is  a  funnel- 
shaped,  muscular  sack,  covered  on  the  inner  surface 
with  a  continuation  of  the  mucous  membrane  of  the 
mouth. 

The  pharynx  is  a  kind  of  common  chamber;  commu- 
nicating with  the  mouth  through  the  fauces,  and  with 
the  nose  by  two  passages  called  the  pos- 
terior nares;  with  the  ears,  by  two  small 
funnel-shaped  openings  called  the  Eusta- 
chi  n  tubes;  with  the  Larynx,  or  voice- 
box,  by  the  glottis,  which  is  closed  by  a 
firm  valve  called  the  epiglottis,  that 
shuts  down  on  it,  and  over  which  the 
food  is  carried  to  the  opening  at  the 
small  end  of  the  funnel,  where  it  termi- 
nates in  the  (Esophagus,  or  gullet. 

27.  (Esophagus  —  its  structure  and 
function. — The  (Esophagus  is  a  tube  ex- 
tending from  the  pharynx  to  the  stomach, 
and  lies  directly  back  of  the  windpipe. 
It  is  made  of  two  coats  or  layers  —  an  in- 
ner covering  of  mucous  membrane,  con- 
tinued downward  from  the  mouth  through 
the  pharynx,  and  an  outer  muscular  coat 
composed  of  a  layer  of  fibers  running 
lengthwise,  and  a  double  set  of  fibers  run- 
ning spirally  around  the  tube  in  each  direction,  and 
consequently  crossing  each  other.  The  longitudinal 
fibers  serve  to  hold  the  tube  steady  in  the  act  of  swal- 
lowing; while  the  oblique  fibers,  contracting  behind  the 
little  ball  of  food,  partly  close  the  tube,  and,  the  closure 

extending  downward,  carries  it  to  the  stomach. 
B.  P.— 3. 


a.  Oblique  fibers. 

6.  Longitudinal 
fibers  exposed. 


24 


PHYSIOLOGY. 


Recapitulation. 

Nutrition  is  that  function  which  supplies  the  material  for  the 
growth  of  the  body,  and  to  repair  its  wastes;  including,  also, 
the  material  for  the  production  of  animal  heat.  This  material 
is  called  food,  and  is  divided  into  the  albuminate  and  carbon- 
aceous classes.  Mastication,  the  first  act  of  nutrition,  is  per- 
formed in  the  mouth,  and  consists  in  grinding  the  food  and 
mixing  it  with  saliva.  The  principal  organs  concerned  in  this 
are  the  teeth  and  the  salivary  glands. 

The  pharynx  receives  the  masticated  food  and  passes  it  into 
f.he  oesophagus,  by  which  it  is  transmitted  to  the  stomach. 


Fio.  8.— THE  STOMACH. 


a 


LESSON    IV. 

DIGESTION. 

28.  Anatomy  of  the  Stomach.  — The  Stomach,  into 

which  the  oesophagus  carries 
the  food,  is  a  curved  sack  or 
bag,  lying  obliquely  across  the 
body  immediately  below  the 
diaphragm,  which  is  a  kind 
of  partition  separating  the 
cavity  of  the  chest  or  thorax 
above,  from  the  abdomen  be- 
low. The  larger  end  of  the 
stomach  lies  in  the  left  side, 
and  its  greater  curvature  or 
rounded  side  is  below. 

On   the   upper  or  concave 

side,  a  little  nearer  the  left  end  of  the  stomach  than  the 
right,  the  oesophagus  enters  it.    This  is  called  the  Cardiac 


a.  Cardiac  orifice.  6.  Pyloric  ori- 
fice,   c.  Pancreatic  duct. 


DIGESTION.  25 

orifice.  Toward  its  right  extremity  the  stomach  be- 
comes narrow,  and  finally  passes  into  the  intestines.  At 
this  point  there  is  a  band  of  muscular  fibers,  which  are 
capable  of  contracting  so  as  to  close  the  opening  entirely. 
This  is  called  the  Pyloric  orifice. 

29.  Functions  of  the   Stomach.  —  The    stomach  is 
composed  of  three  coats.     The  inner  or  mucous  coat  is 
a  continuation  of  that  of  the  oesophagus,  though  differ- 
ing from  it  in  many  particulars.    It  is  very  delicate  and 
soft  like  velvet,  and  besides  the  little  mucous  glands  or 
follicles   it  has  a  number  of  more  complicated  glands, 
whose  mouths,  opening  on  its  surface,  throw  into  the 
stomach  a  thin  acid-fluid  (the  gastric  juice)  as  often  as 
food  is  taken.     This  gastric  fluid,  besides  the  acids  dis- 
solved in  it,  contains  also  a  peculiar  substance  called 
pepsin,  which,  with  the  aid  of  a  uniform  heat,  enables  it 
to  dissolve  albuminate  food. 

30.  Muscular  and  Peritoneal  Coats  of  the  Stomach. 

— The  second  coat  of  the  stomach  is  a  strong,  muscular 
envelope,  consisting  of  two  sets  of  fibers — one  running 
from  end  to  end  of  the  organ,  and  another  running  around 
it,  and  crossing  the  first  nearly  at  right  angles.  The  third 
coat  of  the  stomach  is  a  serous  membrane  —  smooth  and 
dense — it  being  a  continuation  of  th:  Peritoneum,  which 
membrane  lines  the  whole  cavity  of  the  abdomen,  and 
covers  all  the  organs  contained  in  it.  This  covering  is 
reflected  off  from  the  lower  surface  of  the  diaphragm  to 
the  outer  surface  of  the  stomach,  at  the  point  where 
the  oesophagus  passes  through  that  partition. 

31.  Process  of  Digestion. — A  strong  sympathy  exists 
between  the  mouth  and  the  stomach,  for  as  soon  as  mas- 
tication commences,  and  the  salivary  glands  begin  to  act 


26  PHYSIOLOGY. 

freely,  the  peptic  glands  of  the  stomach  pour  out,  at 
their  numerous  mouths,  the  gastric  juice,  ready  to  re- 
ceive the  food  when  it  arrives. 

As  soon  as  this  reaches  the  stomach,  the  muscular 
coats  of  that  organ  begin  to  contract,  gently  rolling  the 
food  from  side  to  side,  thus  mixing  it  thoroughly  with 
the  gastric  fluid  constantly  exuding  from  the  inner  coat 
of  the  stomach.  In  the  meantime,  the  salivary  glands 
are  actively  furnishing  saliva,  which  is  slowly  convert- 
ing the  starchy  part  of  the  food  into  sugar,  and  thus 
dissolving  it. 

32.  Formation  of  Chyme.— This  action  of  the  sali- 
vary glands  has   more   of  importance   than   is   usually 
attached  to  it.     The  poisoning  of  the  saliva  by  a  quid 
of  tobacco  or  a  cigar,  thus  interfering  with  an  important 
part  of  the   process  of  digestion,  is  one  of  the  fruitful 
sources  of  dyspepsia,  however  little  the  unfortunate  vic- 
tim may  suspect  it. 

The  digestive  action  continues  from  two  to  four 
hours,  according  to  the  nature  of  the  food,  the  healthy 
condition  of  the  organs  engaged  in  the  work,  and  the 
general  vigor  and  activity  of  the  body.  The  food  thus 
acted  on  becomes  a  semi-fluid  mass,  nearly  of  a  uni- 
form character,  however  various  and  unlike  the  original 
material  may  have  been.  This  substance,  called  Chyme, 
is  now  ready  to  be  passed  through  the  pylorus  into 
the  intestines,  where  it  enters  on  the  third  and  last 
stage  of  digestion. 

33.  Anatomy  of  the  Intestinal  Canal.— The  Intes- 
tinal canal  is  a  tube,  varying  in  length  from  twenty- 
five   to   thirty  feet,   or   even   more   than   this   in  some 
individuals.      This  tube  is  divided    into  two  sections, 


DIGESTION. 


27 


the  small  intestines  and  the  large.  The  first  section, 
or  small  intestines,  are  divided,  for  the  sake  of  con- 
venience in  describing  them,  into  three  portions,  called 
the  Duodenum,  Jejunum,  and  Ileum. 

The  canal,  in  all  its  parts,  has  an  inner  mucous- 
membrane,  a  middle  muscular  coat,  much  thinner  than 
that  of  the  stomach,  and  an  outer  covering  of  serous 
membrane,  the  peritoneum,  it  being  a  continuation  of 
that  which  covers  the  stomach. 


34.  Laeteals  and  Mesentery. — This  peritoneal  cover- 
ing is  reflected  off 
from  the  tack  part 
of  the  tube,  in  its 
whole  length,  form- 
ing a  double -fold 
of  the  membrane 
called  the  Mesen- 
tery, which  binds 
the  whole  intesti- 
nal apparatus  firm- 
ly to  the  posterior 
wall  of  the  abdo- 
men. The  space 
between  these  folds 
of  the  peritoneum, 
forming  the  mesen- 
tery, is  filled  with  a.  Small  intestines.  6.  Laeteals.  o.  Mesen- 
a  liet-WOrk  Of  blood-  teric  glands,  d.  Mesentery,  e.  Lymphatic 
vessels.  /.  Thoracic  duct.  y.  Aorta. 

vessels,  nerves,  and 

a  class  of  vessels  called  Laeteals.  These  vessels,  com- 
municating with  the  mucous  surface  of  the  intestines, 
carry  a  milky  fluid  containing  the  nutritious  part  of 


28 


PHYSIOLOGY. 


the  food  in  a  dissolved  state.  The  lacteals,  in  their 
passage  through  the  mesentery,  form  clusters  called 
mesenteric  glands,  in  which  the  lacteal  fluid  undergoes 
an  important  change,  by  which  it  acquires  many  of 
the  properties  of  blood. 

35.  Colon  and  Ileo-colic  Talve.  —  The  large  intest- 
ines differ  materially  in  their  form  from  the  small. 
There  are  contractions  at  short  intervals,  diminishing 
the  size  of  the  tube  at  those  points,  and  forming  an 
enlargement  or  kind  of  cell  between  them.  The  small 
intestines  do  not  enter  the  large  tube  in  a  continuous 
line,  but  appear  as  if  the  ileum  was  spliced  on  the  side 
of  the  large  intestine,  at  a  point  three  or  four  inches 
from  its  end.  At  this  junction  the  lips  of  the  open- 
ing are  elongated  inward,  so  as  to  form  a  very  perfect 
valve,  which  permits  the  contents  of  the  small  in- 
FIG.  IO.-ILKO-COI.IC  VALVE,  testines  to  pass  into  the  large, 

but  arrests  all  passage  in  the 
opposite  direction.  This  is 
the  Ileo-colic  valve. 


36.  Direction  of  the  Co- 
lon.—  The  closed  end  of  the 
intestine  lying  back  of  this 
valve  is  called  the  Caecum, 
and  that  portion  which  lies 
forward  of  it  is  the  Colon. 
This  is  divided  into  three 


d 


a.  Ileum.    b.  The  valve,    c.  As- 
cending colon,    d.  Opening  of     sections —  the     ascending    CO- 
appeudix.  -,  .    .  .    ,   .       .  , 

Ion,  rising  on  the  right   side 

nearly  to  the  stomach;  the  transverse  colon,  extend- 
ing across  the  abdomen  below  the  stomach;  and  the 
descending  colon,  passing  down  the  left  side  to  the 


DIGESTION. 


29 


rectum,  which  is  the  last  division   of  the  large  intes- 
tines, and  the   termination  of  the  intestinal  canal. 


Fio.  11.— INTESTINAL  CANAL. 

e 


a.  Duodenum.    6.  Ileum.   c.  Ccecum.   d.  Ascending  colon,   e.  Transverse 
colon.   /.  Descending  colon,    g.  Rectum,    h.  Vermiform  appendix. 

37.  The  Liver— its  function.— The  Liver,  the  largest 
gland  of  the  body,  is  situated  immediately  below  the 
diaphragm,  and  chiefly  on  the  right  side  of  the  body. 
Its  office  (which  will  be  more  particularly  described 
hereafter)  is  to  separate  from  the  blood  a  slightly  tena- 
cious yellow  fluid,  called  bile,  which  is  collected  into 
the  gall  bladder,  and  from  thence  passed  into  the  duo- 
denum, a  short  distance  below  the  stomach. 

The  Pancreas  is  a  long,  slender  gland,  lying  under 
tlu  convex  surface  of  the  stomach,  and  secreting  a 


30 


PHYSIOLOGY. 


fluid  very  nearly   resembling   saliva,  which    it   throws 
into  the  duodenum. 

FIG.  12.— THE  LIVKU. 
d  ft 


a.  Eight  lobe  of  the  liver.    6.  Left  lobe.    c.  Vena  cava.    d.  Gall  bladder. 
e.  Portal  vein.   /.  Bile  duct.    g.  Hepatic  artery. 

38.  Digestive  Process.  The  Spleen.  — The  food 
being  converted  into  chyme  in  the  stomach,  and 
passed  through  the  pylorus  into  the  duodenum,  is 
mixed  with  the  pancreatic  fluid  which  serves  to  di- 
lute it,  and  perhaps  complete  the  work  of  the  saliva 
in  converting  the  starch  into  sugar.  The  bile  being 
alkaline,  from  the  soda  which  it  contains,  neutralizes 
any  acid  which  the  chyme  may  have  brought  from 
the  stomach;  and  it  also  has  an  effect  on  the  oily 
portions  of  the  food,  so  as  to  make  them  dissolve 
readily. 

These  changes  convert  the  chyme  into  chyle,  which, 
as  a  milky  fluid,  is  absopfe^^y  the  lacteal  vessels, 
and  transmitted  through  the  mfcseinteric  glands  into 
the  Thoracic  duct,  which  is  the  common  trunk  of  all 
the  lacteals.  This  vessel  carries  the  lacteal  fluid  up- 
wurd,  and  pours  it  into  the  large  vein  which  returns 
the  blood  from  the  left  arm.  A  little  to  the  left,  and 


CIRCULATION.  31 

below  the  great  curvature  of  the  stomach,  lies  the 
Spleen.  It  is  made  up  chiefly  of  a  net-work  of  blood- 
vessels. Its  use,  in  the  animal  economy,  has  not  been 
clearly  determined. 

Recapitulation. 

The  stomach  is  composed  of  three  coats :  an  inner  mucous  coat, 
a  middle  muscular  layer,  and  an  outer  serous  membrane.  The 
function  of  the  stomach  is  to  change  the  various  forms  of  food 
into  a  homogeneous  mass,  and  to  render  it  soluble  in  water. 
This  semi-fluid  mass  is  called  chyme.  The  intestinal  canal  is 
divided  into  two  sections  —  the  large  and  the  small  intestines. 
The  mesentery,  a  double  fold  of  the  peritoneum,  binds  the  in- 
testines to  the  posterior  wall  of  the  abdomen,  and  contains  the 
lacteal  vessels  between  its  folds.  The  liver  secretes  bile,  which 
acting  on  the  chyme,  converts  it  into  chyle. 


LESSON    V. 


-^v 
CIRCULATION. 


39.  The   Apparatus  of  the  Circulation.  — Having, 

in  the  last  lesson,  followed  the  food  through  the  first 
stage  of  preparation  for  nutrition,  we  now  find  it,  if 
the  work  of  digestion  has  been  well  done,  prepared  to 
enter  the  circulation,  that  it  may  be  carried  to  all 
parts  of  the  living  body — to  supply  material  for  its 
growth  in  early  life,  and  its  repair  at  all  times.  This 
work  of  distributing  the  nutriment  prepared  by  the 
changes  it  has  undergone  in  the  mouth,  stomach,  and 
intestines,  to  become  a  part  of  the  living  tissues,  is 
performed  by  the  Heart,  Arteries,  Capillaries,  and  Veins. 


32  PHYSIOLOGY. 

The  heart  consists  of  a  right  and  left  side,  separated 
from  each  other  by  a  strong  partition,  which,  after 
birth,  is  entirely  closed,  so  that  there  is  no  more  com- 
munication between  the  right  and  left  cavity  than  if 
the  two  sides  were  distinct  and  separate  hearts. 

40.  Anatomy  of  the  Heart. — Each  side  is  composed 
of  two  chambers  or  cavities,  capable  of  holding  about 
two  ounces  of  blood   each.      The  first  or  upper  one  of 
these  chambers  is  called  the  Auricle,  and  the  lower  one 
the    Ventricle;    and    the    two    auricles    and    ventricles 
are  distinguished  from  each  other   by  the   terms  right 
and   left.     The    right    side    of   the    heart    receives    the 
blood  returning  from   all  parts  of  the   body,  and  sends 
it  to  the  lungs  to  be  purified  and  materially  changed, 
from    whence    it    is   returned    to    the   left    side  of   the 
heart  to  be  distributed  again  throughout  the  system. 

The  lungs  being  near  by  the  heart,  the  right  side 
has  much  the  lighter  task,  though  the  quantity  of 
blood  sent  out  from  each  side,  in  a  given  time,  is  the 
same.  From  this  cause  the  walls  of  the  right  side  of 
the  heart  are  much  thinner  than  on  the  left. 

41.  Position  of  the  Heart.  —  The  heart  is  situated 
in    the   lower   part   of   the   chest,  between  the  folds  of 
the  partition  separating  the  lungs  from  each  other.     It 
is  a  cone-shaped  organ,  with  the  base  or  large  end  di- 
rected   upward    and    backward,    pointing    toward    the 
right   shoulder,  while   the   apex  or   small   end  projects 
downward,  forward,  and   to  the   left   side. 

When  in  vigorous  motion,  the  point  of  the  heart 
strikes  against  the  front  wall  of  the  chest,  and  can  be 
felt  distinctly  near  the  fifth  rib  on  the  left  side.  Its 
under  side  rests  on  the  arch  of  the  diaphragm,  which 


CIRCULATION. 


33 


separates  the  chest  from  the  abdomen.  The  heart  is 
inclosed  in  a  membranous  sac  called  the  pericardium, 
between  the  inner  surface  of  which  and  the  heart  there 
is  always  a  small  quantity  of  water,  which  serves  to 
protect  the  heart  from  the  effect  of  blows  on  the  chest, 
or  sudden  movements  of  the  body. 


FIG.  13.— FRONT  VIEW  OF  TIIK 
HKAKT. 


42.  Action  of  the  Heart.  —  The  blood  reaches  the 
right  auricle  as  it  is  returned 

from  the  veins;  and  by  the 
contraction  of  the  auricle,  the 
venous  blood  is  forced  into  the 
ventricle,  through  three  tri- 
angular folds  of  a  membrane. 
These  are  called  the  Tricuspid 
valves,  and  they  are  so  ar- 
ranged as  to  permit  the  blood 
to  pass  freely  toward  the  ven- 
tricle, but  close  so  as  to  arrest 
its  passage  in  the  opposite  di- 
rection. 

The  ventricle  being  now 
filled,  contracts  on  its  con- 
tents, and  the  blood  is  forced 
into  the  Pulmonary  artery, 
by  which  it  is  carried  to  the 
lungs.  After  passing  the  pul- 
monary capillaries,  and  under- 
going a  change  of  which  we  shall  speak  in  the  proper 
place,  it  is  returned  to  the  heart  by  the  pulmonary 
vein. 

43,  Talves  of  the  Heart  and  their  use. —  Entering 
the  left  auricle,  the   blood   is  transmitted   through  the 


a.  Right  ventricle.  6.  Left  ven- 
tricle, c.  Right  auricle,  d. 
Left  auricle,  e,  e,  t,  e.  Pul- 
monary veins.  /.  Pulmo- 
nary artery,  g.  Aorta,  h. 
Vena  cava. 


34 


PHYSIOLOGY. 


FIG.  14.— VALVES  OF  THE  HEAIIT. 


a.  Left  auricle.  6.  Right  auricle. 
c.  Left  ventricle,  d.  Right  ven- 
tricle. /.  Mitral  valves,  g.  Tri- 
cuspid  valves. 


valves,  which,  on  this  side  of  the  heart,  consist  of  two 

membranous  folds  called 
Mitral  valves,  into  the  left 
ventricle,  whose  walls  con- 
sist of  a  firm  and  power- 
ful muscle.  It  is  now  con- 
tracted, and  the  blood, 
propelled  with  consider- 
able force,  is  thrown  into 
a  large  tube  called  the 
Aorta. 

This  tube  may  be  taken 
as  the  representative  of 
the  whole  class  of  blood- 
vessels whose  office  it  is 
to  carry  the  blood  from  the 
heart.  They  are  called  Arteries,  while  those  vessels  which 
return  the  blood  to  the 
heart  are  named  Veins. 
The  blood  having  en- 
tered the  aorta,  is  pre- 
vented from  returning 
to  the  ventricle,  when 
that  cavity  expands,  by 
three  folds  of  the  inner 
coat  of  the  artery,  which 
from  their  shape  are  call- 
ed Semi-lunar  valves. 

44.  Arteries,  Capil- 
laries, and  Yeins  — 
their  anatomy.  —  The 
arteries  are  firm,  elastic 
tubes,  made  of  three  coats.  The  external  coat  is  of  a 


FIG.  15.— SEMI-LUNAR  VALVES. 


a.  A  section   of  the  aorta  laid   open. 
6.  The  semi-lunar  valves. 


CIRCULATION.  35 

spongy,  cellular  texture ;  the  middle  coat  is  of  very  dense, 
fibrous  material,  generally  regarded  as  muscular;  the 
inner  coat  is  a  smooth  and  very  fine  serous  mem- 

mm 

brane,  beinggpi  continuation,  from  the  heart,  of  the 
lining  memlS'ane  of  the  ventricle.  The  aorta  sends  off 
branches  to  all  the  living  organs  of  the  body;  even 
the  heart  itself  receives  a  pair  of  arteries  from  the 
aorta,  to  carry  to  it  material  for  its  repair. 

These  branches,  as  they  divide  and  sub-divide,  grow 
constantly  smaller,  but  more  numerous,  till  at  last  they 
/terminate  in  a  net- work  of  hair-like  vessels,  called 
/  Capillaries,  almost  infinite  in  number.  These  vessels 
ve  origin  to  the  system  of  veins  which,  running  into 
h  other,  become  less  and  less  numerous,  till  finally 
they  form  one  great  trunk,  the  Vena  Cava,  through 
\  which  all  the  veins  of  the  general  circulation  com- 
^unicate  with  the  heart. 

45.  Forces  concerned  in  the  Circulation.  —  Several 
forces  are  concerned  in  the  circulation  of  the  blood,  the 
first  and  chief  of  which  is  the  contraction  and  expan- 
sion of  the  heart.  Though  the  heart  is  a  double  organ, 
and  concerned  in  carrying  on  two  distinct  circulations 
— one  to  the  lungs  and  the  other  te-4he  general  sys- 
tem—  yet  all  its  parts  work  in  concert. 

The  two  auricles  contract  at  one  time,  and  while 
they  are  contracting,  the  ventricle  is  expanded  on  each 
side;  but  as  soon  as  these  are  filled  with  blood,  they 
begin  to  close  the  cavity,  and,  by  a  powerful  contrac- 
tion, the  contents  of  each  ventricle  is  injected  into  the 
artery  united  with  it.  While  this  is  going  on,  the 
auricles  are  expanded  to  receive  the  constant  stream 
of  blood  returned  by  the  great  veins. 


36  PHYSIOLOGY. 

46.  The  Pulse.  —  Each  contraction  of  the  ventricle 
gives  a  wave-like  motion  to  the  blood  in  the  arteries. 
This  is  the  Pulse.  It  is  probably  assisted  by  a  con- 
traction of  the  artery  itself,  following  directly  after  the 
wave  of  blood.  The  changes  which  are  made  in  the 
condition  of  the  blood  while  passing  through  the  capil- 
laries, evidently  exert  a  force  in  transmitting  it  through 
these  minute  passages.  This  force  is  entirely  independ- 
ent of  the  contraction  of  the  heart.  The  blood  is  thus 
constantly  forced  into  the  veins;  these  vessels,  being 
filled,  must  overflow  into  the  right  auricle.  The  veins 
are  passive  in  the  work  of  circulation. 

Recapitulation. 

The  circulation  is  carried  on  by  the  heart,  arteries,  veins,  and 
capillaries.  The  heart  is  a  double  organ,  consisting  of  a  right 
and  left  side,  and  each  side  is  composed  of  an  auricle  and  a 
ventricle.  The  heart  is  inclosed  in  a  sac — the  pericardium  — 
and  lies  in  the  partition  separating  the  lungs,  its  larger  end 
looking  upward  and  backward,  and  its  smaller  downward  and 
forward.  Valves  are  interposed  between  the  auricles  and  ven- 
tricles on  each  side  of  the  heart.  The  arteries  convey  the 
blood  from  the  heart,  and  the  veins  return  it  to  that  organ. 
The  capillaries  unite  the  arteries  with  the  veins.  The  con- 
traction and  expansion  of  the  heart  is  the  chief  force  concerned 
in  the  arterial  circulation. 


LESSON   VI. 

CIRCULATION.  —  CONTINUED. 

47.  Yeins  —  their  Yalves. — The  veins  originating  in 
the  net-work  of  capillaries,  and  joining  together,  form 


CIRCULATION.  37 

constantly  enlarging  trunks;  but  these,  unlike  the  ar- 
teries, are  soft  and  easily  compressed.  The  middle  or 
fibrous  coat  is  almost  entirely  wanting,  and  <4he  two 
remaining  coats  are  much  thinner  than  those  of  the 
arteries.  When  emptied  of  their  contents,  the  arteries 
remain  open  tubes;  but  the  veins,  under  similar  circum- 
stances, collapse  —  the  walls  falling  in  on  each  other. 

At  irregular  intervals,  the  internal  coat  of  the  veins 
forms  pouches  or  folds,  which  operate  most 


effectually   as    valves.     They   are    so   ar-  FIG.  IB.- 

,      ,.    ,.  ,       OF  THE  VEINS. 

ranged  that  the  open  end  of  the  pouch 
is  turned  toward  the  heart,  and  when 
the  blood  flows  in  that  direction,  the 
valve  closes  down  against  the  wall  of 
the  vein;  but  an  attempt  to  force  a  flow 
in  the  opposite  direction,  fills  the  pouch 
with  blood,  and,  by  its  enlargement, 
closes  the  vein  completely. 

IS.  Yenous   Circulation  effected   by  a'  A  vein  laid 

__  •        T_    •  open,  exposing 

Muscular  Movements.  —  The  veins  being      the  valves. 
soft,    and    passing    freely    through    and 
among   the   moving  machinery   of   the   body,  are   con- 
stantly compressed  by  these  movements,  and  the  valves 
preventing   this    compression    from   forcing    the    blood 
backward  into  the  capillaries,  become  material  aids  in 
transmitting  the  blood  through  the  veins. 

It  is  sometimes  important  to  be  able  to  distinguish 
a  vein  from  an  artery  at  once.  When  the  vessel  is 
opened  and  blood  is  issuing  from  it  —  if  it  be  an  artery, 
it  will  flow  in  intermittent  jets  corresponding  to  the  pul- 
sations of  the  heart  ;  if  it  be  a  vein,  the  flow  will  be  a 
constant  stream.  If  the  vessel  be  not  opened,  the  pulsat- 


38  PHYSIOLOGY. 

ing  motion  may  be  seen  or  felt  even  in  a  small  artery, 
but  in  a  vein  no  such  movement  is  perceptible. 

49.  Lymphatic  Vessels — their  functions. — There  is 

another    class    of    vessels,    called    Lymphatics,    which 

perform  an  important  office   in   the   circulation.     They 

resemble    small    veins    in    their    general 

FIG.  17.-A  LYM-  stmcture    but   Carrv  a   transparent   fluid 

PHATIC  VESSEL  *  r 

MAGNIFIED.  instead  of  blood.  Their  valves  are  more 
numerous  than  those  of  the  veins,  and  the 
small  tubes  show  but  little  disposition  to 
unite,  often  running  parallel  with  each 
other,  in  clusters,  for  some  distance.  In 
some  parts  of  the  body,  as  about  the  neck, 
groins,  and  armpits,  the  lymphatics  form 
numerous  clusters  or  balls,  called  lym- 
phatic glands.  These  are  the  principal 
seat  of  scrofulous  diseases.  In  their  struct- 
ure they  are  much  like  the  mesenteric 
glands. 

The  lymphatics  are  chiefly  employed 
in  taking  up  and  conveying  to  the  blood- 
vessels the  waste  matter  resulting  from 
the  constant  wear  of  the  tissues.  They  all  communi- 
cate with  the  venous  side  of  the  circulation,  so  that 
the  blood  with  which  the  lymphatic  circulation  is 
mingled  is  not  sent  out  into  the  general  circulation 
till  it  has  been  purified  in  the  lungs.  No  lymphatics 
have  yet  been  detected  in  the  brain,  in  tendon,  carti- 
lage, or  bone.  In  these  tissues  the  office  of  the  lym- 
phatics is  probably  performed  by  veins.  The  lacteals, 
in  their  general  character  and  work,  very  much  re- 
semble lymphatics. 


CIRCULATION.  39 

50.  Absorbents  —  their    action.  —  A   class   of   lym- 
phatic vessels,  called  Absorbents,  are   engaged  in  the 
business  of  taking  up  fluids  from  the  external  surface 
of  the  body,  and  the  surface  of  internal  cavities.     Vari- 
ous kinds  of  liquids,  when  applied  to  the  skin,  can  be 
detected  in  the  circulation,  and  in  the  different  secre- 
tions, in  a  very  short  time.     In  the  same  manner,  sub- 
stances inhaled  are  taken  up  by  the   absorbents,  and 
carried  directly   into  the  blood-vessels,  to  be   mingled 
with  all  the  fluids  of  the  body.     In  this  manner  poisons 
are  often  imbibed  and  diseases  contracted,  without  the 
slightest  suspicion  of  the  manner  of  taking  the  poison. 

51.  Absorbents   in    Serous    Membranes.  —  Another 
office  of  the  absorbent  vessels  is  to  take  up  and  carry 
away  the  fluids  constantly  exhaled  from  the  surface  of 
membranes  lining  cavities.     There  is,  in  a  healthy  state 
of  these  serous  membranes,  a  very  nice  adjustment  in 
the  work  done  by  the  exhalent  and  absorbent  vessels,  so 
as  to  keep  the  surface  constantly  moistened,  and  yet  suf- 
fer no  accumulations  of  fluids  in  such  cavities.     Dropsy 
is  but  the  disturbance  of  this  nicely  balanced  exhala- 
tion and  absorption.  '     > 

Simple  fluids,  like  water,  are  not  subject  to  any 
change  in  the  stomach,  nor  do  they  take  the  circuitous 
route,  by  way  of  the  lacteals  and  thoracic  duct,  to  the 
circulation,  but  are  absorbed  directly  from  the  surface 
of  the  stomach,  and  pass  into  the  veins  at  once.  Even 
alcohol  or  turpentine,  taken  into  the  stomach,  can  be 
detected  in  the  air  breathed  from  the  lungs,  in  a  very 
short  time  after  it  is  swallowed. 

52.  Anastomosing  Tessels. — The  vessels  constituting 

the  circulatory  apparatus,  whether  arteries,  veins,  capil- 
B.  P.— 4. 


40  PHYSIOLOGY. 

laries,  or  lymphatics,  often  communicate  by  collateral 
branches,  but  always  with  vessels  of  their  own  kind. 

By  means  of  these  vessels,  called  Anastomosing 
branches,  the  surgeon  is  able  to  preserve  the  life  of  a 
part,  though  he  may  be  required  to  tie  the  principal 
artery  supplying  that  part  with  blood.  An  anastomos- 
ing branch,  connecting  the  injured  vessel  below  the 
ligature  with  a  neighboring  artery,  will  furnish  a 
partial  supply  of  blood;  and  becoming  enlarged  by  the 
increased  work  it  is  required  to  do,  the  anastomosing 
vessel  soon  acquires  the  capacity  of  the  original  trunk, 
and  performs  its  office  effectually. 

Recapitulation. 

The  heart  is  a  double  organ,  carrying  on  two  circulations  at  the 
same  time. 

The  right  side  of  the  heart  is  devoted  to  the  pulmonary  circula- 
tion, or  that  carried  on  through  the  lungs  for  the  purpose  of  puri- 
fying and  oxidizing  the  blood. 

The  left  side  of  the  heart  is  engaged  in  the  distribution  of  the 
blood  to  all  parts  of  the  body,  for  its  nutrition. 

In  health  the  heart  makes  about  seventy-five  contractions  in 
a  minute. 

Arteries  carry  the  blood  from  the  heart  —  veins  return  it  to  that 
organ. 

Capillaries  connect  the  extremities  of  the  arterial  and  venous 
circulations;  hence  all  arteries  terminate  in  capillaries,  and  all 
veins  have  their  origin  there. 

The  change  from  arterial  to  venous  blood  takes  place  in  the 
capillaries  of  the  general  circulation,  and  the  opposite  change  in 
the  capillaries  of  the  pulmonary  circulation. 


RESPIRATION.  41 


LESSON   VII. 

N  RESPIRATION. 

x  53.  The  Respiratory  Organs  aiid  their  use.—  The 
respiratory  apparatus  consists  of  a  trachea  or  wind- 
pipe, two  lungs,  the  bronchial  tubes,  and  air-cells. 
Auxiliary  to  these  are  the  ribs,  and  the  muscles  be- 
tween them;  the  diaphragm,  and  the  abdominal  mus- 
cles. The  purpose  of  this  rather  complicated  apparatus 
is  two-fold:  first,  to  impart  to  the  blood  oxygen,  which 
is  one  of  the  constituents  of  the  air;  and,  second,  to 
relieve  the  blood  of  carbonic  acid  and  watery  vapor, 
which  it  has  acquired  in  passing  through  the-  capilla- 
ries, and  which  has  resulted  from  the  decomposition  of 
the  worn-out  particles  of  the  body  and  of  the  carbona- 
ceous food. 

M.  Position  of  the  Lungs.  —  The  body  or  trunk  is 
divided  into  two  great  cavities.  In  the  abdomen  or 
lower  one  of  these  is  placed  the  digestive  apparatus, 
which  we  have  already  described.  The  upper  one  is 
devoted  to  the  Heart  and  great  blood-vessels,  which  are 
situated  in  the  space  between  the  walls  of  a  double 
partition  that  completely  separates  the  cavity  into 
two  apartments;  and  to  the  Lungs,  one  of  which  fills 
each  of  these  apartments.  This  cavity  is  called  the 
Thorax  or  Chest.  Unlike  the  abdomen,  it  is  surrounded 
by  bony  walls  on  all  sides,  except  the  bottom,  where 
it  is  separated  from  the  abdomen  by  the  diaphragm. 
The  natural  shape  of  the  chest  is  that  of  a  cone,  with 
its  small  end  upward,  and  its  base  resting  on  the  dia- 
phragm below. 


42 


PHYSIOLOGY. 


FIG.  18.— RESPIRATORY  APPARATUS. 


,f\ 


55.  Trachea  and  Bronchia. — The  Trachea  is  a  tube 
extending  from   the   air-passages  of   the  nose   and   the 
mouth  to  a  point  nearly  opposite  the  top  of  the  breast- 
bone,   where    it    separates    into    two   branches,    which, 
from   this   point,  take   the   name   of   Bronchia.     These 
bronchial  tubes  divide  and  sub-divide  as  they  distribute 
themselves  through   the   lungs  —  each   tube  finally  ter- 
minating in  a  little 
sac  called  an  air-cell. 
These  tubes,  both  the 
trachea  and  bronchia, 
are  composed  of  rings 
formed  of  a  hard,  elas- 
tic  substance,  called 
cartilage.   In  the  tra- 
chea the  rings  are  not 
quite   closed   on   the 
back  part,  thus  leav- 
ing   a    soft    side    to 
the  tube  for  the   ac- 
commodation of  the 
sesophagus,       which 
lies  immediately  be- 
hind it. 

56.  Air-Ceils    and    their    use.— The    trachea    and 
bronchial  tubes  are  lined  with  a  very  delicate  mucous 
membrane,  which    is   extended   into   the    air-cells.     On 
this   membrane,  forming   the   inner  surface  of  the  air- 
cells,  is   spread   out  a  net- work  of   capillary  vessels — 
the  terminations  of  the  pulmonary  artery.     This  mem- 
brane  permits   gases   to   pass   through   it   readily,   and 
thus  the  oxygen  from  the  air  in  the  air-cells  is  trans- 
mitted to  the  blood;    and  the  carbonic  acid  contained 


a.  Larynx,    b.  Trachea,    c.  Left  lung. 
d.  Right  lung.    e.  Heart. 


RESPIRATION. 


43 


FIG.  19.— AIK-CEL.I.S. 


in   the   blood-vessels   passes   in   the   opposite   direction, 
and  escapes  with  the  air  exhaled  from  the  lungs. 

Pure  air  is  nearly  one-fifth  oxy- 
gen, and  four-fifths  nitrogen.  These 
gases  are  not  combined  together, 
but  are  merely  in  a  state  of  mix- 
ture. When  the  air  is  taken  into 
the  lungs,  it  contains  about  twenty- 
one  per  cent  of  oxygen,  but  it 
is  returned  with  but  about  seven- 
teen per  cent;  the  loss,  however, 
is  filled  by  nearly  four  per  cent  of  carbonic  acid  and 

FIG.  20.— DIAPHKAGM. 


a,  a.  Cavity  of  the  right  and  left  lungs.     6,  6.  Ends  of  the  ribs,  which 
are  removed  to  expose  the  diaphragm,    c,  c.  Arch  of  the  diaphragm. 

watery  vapor.     This  proportion  varies  a  little  in  dif- 
ferent   individuals,    and    in    the    same    individual    in 


44  PHYSIOLOGY. 

different  states  of  health;  but  this  is  about  the  average 
result  in  a  healthy  person. 

57.  Mechanism  of  Respiration.     Diaphragm.  —  In 

the  act  of  breathing,  the  lungs  are  passive,  the  air 
being  drawn  in  by  the  enlargement  of  the  chest,  made 
by  the  action  of  the  Diaphragm  and  the  muscles  be- 
tween the  ribs. 

The  diaphragm  is  the  floor  of  the  chest.  It  is  com- 
posed of  at  least  two  layers  of  muscles,  covered  on  its 
under  side  by  the  peritoneum,  and  above  by  the  pleura, 
a  serous  membrane  lining  the  cavity  of  the  chest,  and 
covering  the  lungs.  The  diaphragm  has  nearly  the 
shape  of  an  inverted  basin,  being  an  irregular  arch  in 
every  direction.  When  the  muscles  composing  the  dia- 
phragm contract,  the  arch  is  shortened,  and  conse- 
quently the  crown  of  it  is  drawn  downward,  and  the 
cavity  of  the  chest  made  deeper  in  proportion. 

FIG.  21.— INTERCOSTAL  MUSCLES. 


a— 


a.  External  iutercostals.  b.  Internal  iutercostals. 

58.  Bibs  and  Intercostal  Muscles.  —  The  ribs  are 
articulated  to  the  spinal  column  by  a  movable  joint, 
and  in  front  they  are  attached  to  the  breast-bone  by 
a  flexible  cartilage.  They  are  curved  around  the  body 


- 


RESPIKATIOK.  46 

like  a  hoop;  but  they  are  also  bent  downward  from 
the  back  and  to  a  little  beyond  the  middle  of  the  rib, 
from  which  they  ascend  to  the  breast-bone.  The  space 
between  the  ribs  is  filled  by  two  layers  of  muscles, 
passing  obliquely  from  one  rib  to  the  other.  They 
are  called  the  external  and  internal  intercostals. 

The  upper  rib,  being  nearly  immovable,  acts  as  a 
fixed  point  to  which  the  whole  series  is  attached  by 
means  of  the  intercostal  muscles.  And  when  these 
contract,  the  middle  of  each  rib  is  drawn  upward,  and 
consequently  the  chest  is  enlarged  in  its  transverse 
diameter. 

59.  How  we  Breathe. — Now,  as  the  lungs  completely 
fill  the  cavity  they  each  occupy,  and  the  fold  of  the 
pleura  covering  the  lungs,  and  that  lining  the  chest, 
are  in  actual  contact,  it  follows  that  the  increased  space 
made  by  enlarging  the  cavity  of  the  chest,  can  be 
filled  only  by  the  air  passing  into  the  air-cells,  and  thus 
enlarging  the  lungs  sufficiently  to  fill  the  enlarged  cav- 
ities they  occupy.  By  this  movement,  about  twenty- 
five  cubic  inches  of  air  are  drawn  in  at  an  ordinary 
respiration. 

But  a  healthy  pair  of  lungs  will  contain,  in  common 
breathing,  about  two  hundred  cubic  inches  of  air,  so 
that  only  about  one-eighth  of  it  is  changed  at  each 
breath.  The  relaxation  of  the  diaphragm  and  inter- 
costal muscles,  though  necessary  for  the  expulsion  of 
the  air  inhaled,  is  not  of  itself  depended  on  in  the 
economy  of  respiration.  From  the  arch  of  the  large 
bone  on  each  side,  which  forms  the  basin-like  cavity 
terminating  the  abdomen  below,  there  arise  several 
muscles  which  form  the  walls  of  that  cavity. .  A-  pair 


46  PHYSIOLOGY. 

of  these  are  attached,  above,  to  the  ribs,  and,  on  con- 
tracting, draw  these  downward.  Other  muscles  run 
transversely  or  obliquely  around  the  abdomen,  which, 
by  their  contraction,  force  the  contents  of  the  abdomen 
upward,  and  thus  elevate  the  arch  of  the  diaphragm, 
and  expel  the  air  inhaled. 

Recapitulation. 

Respiration  is  carried  on  by  means  of  the  trachea  and  lungs, 
The  lungs  consist  chiefly  of  bronchial  tubes,  air-cells,  and 
blood-vessels.  The  ribs  and  their  muscles,  the  diaphragm  and 
the  abdominal  muscles,  give  the  movements  in  breathing.  The 
lungs  are  entirely  separated  by  a  double  partition.  Respiration 
supplies  oxygen  to  the  blood,  and  removes  impurities  from  it. 
These  changes  take  place  in  the  air-cells.  The  cavities  contain- 
ing the  lungs  are  enlarged  by  the  contraction  of  the  diaphragm 
depressing  its  arch,  and  by  the  elevation  of  the  ribs  increasing 
the  lateral  dimensions.  The  space  thus  made  is  filled  by  air 
passing  through  the  trachea  and  bronchia.  The  contraction  of 
the  abdominal  muscles  elevates  the  arch  of  the  diaphragm,  and 
thus  expels  the  air. 


LESSON    VIII. 

RESPIRATION  —  PURIFICATION   OF   THE   BLOOD. 

60.  Two-fold  Purpose  of  Respiration. — Respiration 
serves  a  two-fold  purpose  in  the  animal  economy.  First, 
it  furnishes  oxygen  to  the  blood.  This  is  carried  by 
the  circulation  to  all  the  tissues  of  the  body,  where  it 
combines  with  the  elements  of  the  old  and  worn-out 
particles,  forming  with  them  new  compounds,  capable 
of  being  dissolved  in  the  blood  and  thus  carried  for- 
ward into  the  veins.  At  the  same  time,  in  the  capil- 
laries, it  comes  into  close  contact  with  the  carbonace- 


RESPIRATION.  47 


ous  elements  of  the  newly  digested  food,  combines  with 
its  carbon,  forming  carbonic  acid,  disengaging  its  other 
elements  to  form  water.  From  these  changes  the  heat 
of  the  body  is  supplied  and  maintained. 

But  these  products,  resulting  from  the  combination 
of  the  oxygen  with  the  tissues  and  with  the  food, 
being  thrown  into  the  circulation,  load  the  blood  with 
impurities.  The  second  purpose  of  respiration  is  to 
relieve  the  blood  of  these  impurities.  All  the  carbonic 
acid  generated  in  the  living  body,  and  a  large  portion 
of  watery  vapor,  as  well  as  numerous  other  substances 
which  find  their  way  into  the  circulation  and  are  in- 
capable of  being  made  a  part  of  the  living  body,  are 
discharged  by  the  lungs. 

61.  Chemical    Changes  — the    Source    of    Animal 
[eat.  —  The     production    of    heat    by    the     chemical 
langes    constantly    taking    place    in    animal    bodies, 

,ppears  to  be  intimately  connected  with  the  evolution 
,and   expenditure   of  force   in   the  body.     Every  move- 
,  ment  of   the  body,  or  any  part  of  it,  requires  a  certain 
amount  of  force  to  accomplish   it,  proportioned   to   the 
, extent   and  violence  of  the   movement;    and*,  as  many 
of  these  motions  are  constant,  and  all  of  them  frequent, 
[  I  /Jthey  demand   a   constant  and   uniform   supply  of  this 
Ay. force.     This  they  have   in   respiration  and   its   results^ 
Hence  it  follows,  that  as  we   increase  the  active  exer- 
cise of  the  body,  there   is  a   corresponding  increase  of 
breathing;   and  more  oxygen  being  thus  distributed  to 
the  tissues,  more  chemical  action  takes  place,  and  from 
is  heat  and  force  are  evolved. 

62.  Products  of  Respiration. — But  all  this  is  con- 
suming both   the   tissues  of  the  body  and  the  carbon- 

B.  P.— 5. 


48  PHYSIOLOGY. 

aceous  elements  of  the  food,  and  this  waste  must  be 
supplied  by  additional  food,  consequently  exercise  in 
the  open  air  increases  the  appetite,  and  invigorates 
all  the  vital  functions,  thus  furnishing  new  material, 
well  prepared  to  replace  the  worn-out  particles  of  the 
tissues,  and  enabling  the  several  organs,  whose  duty  it 
is  to  carry  off  and  dispose  of  the  old  matter,  to  do  that 
work  effectually.  A  large  proportion  of  this  waste  is 
converted  into  carbonic  acid,  which  is  formed  by  the 
direct  union  of  the  oxygen  inhaled,  and  the  carbon  of 
the  tissues.  This  being  carried  to  the  lungs,  escapes 
with  the  air  exhaled  in  respiration. 

If  we  fill  a  vessel  with  clear  lime-water,  and,  through 
a  tube,  blow  our  breath  into  it,  we  shall  soon  perceive  it 
becoming  milky  from  the  carbonic  acid  of  the  breath 
combining  with  the  lime.  The  hydrogen,  another  ele- 
ment of  the  worn-out  particles,  unites  also  with  the 
oxygen  communicated  to  the  blood  in  breathing,  and 
thus  forms  water,  a  great  part  of  which  is  thrown 
off  from  the  lungs  as  vapor. 

63.  Other  Means  of  Purifying  the  Blood.— Other 
portions  of  this  waste  material,  rendered  fluid  by  com- 
bination with  oxygen,  are  taken  up  by  the  absorbents, 
and  carried  into  the  circulation,  from  which  they  are 
separated  by  the  process  of  secretion.  This  operation 
is  performed  by  a  class  of  organs  called  Glands.  The 
largest  gland  of  the  body  is  the  liver,  whose  duty  it  is 
to  separate,  from  the  venous  blood  circulating  through 
it,  a  peculiar  fluid,  the  bile,  which,  as  we  have  learned 
(§  38),  performs  an  important  office  in  the  conversion 
of  chyme  into  chyle.  A  large  part  of  the  bile,  in  per- 
forming this  work,  is  itself  changed  into  sugar,  in 


RESPIRATION. 


49 


FIG.  22.— PERSPIRATORY 


which  form  it  re-enters  the  circulation  as  a  carbonace- 
ous element  of  the  blood.   The 
remainder  of  the  bile,  which 
is  incapable  of  this  change,  is 
passed  off  as  excrement. 

The  Skin  is  another  impor- 
tant outlet  of  the  wastes  of 
the  living  body.  A  cluster  of 
small  glands  forms  the  lower 
surface  of  the  skin,  and  from 
each  gland  a  small  tube,  called 
a  perspiratory  duct,  winds  its 
way  in  a  spiral  course  through 
the  skin  to  its  external  sur- 
face. The  mouths  of  these 
form  what  are  commonly  call- 
ed the  pores  of  the  skin.  The 
perspiration  consists  chiefly 
of  water,  with  various  saline 
matters  dissolved  in  it.  Under  ordinary  circumstances, 
it  passes  off  in  the  form  of  vapor,  and  is  called  insen- 
sible perspiration,  because  it  is  not  observed;  but  when 
the  secretion  becomes  more  active,  it  is  liquid,  forming 
drops  of  sweat. 

64.  The    Skin.     Perspiratory  and    Oil    Glands.  - 

Another  set  of  glands  are  located  near  the  surface  of 
the  skin,  smaller  and  much  simpler  than  the  perspira- 
tory glands.  They  are  the  oil  glands,  or  sebaceous  follicle*, 
which  furnish  oil  to  keep  the  surface  of  the  skin  soft 
and  pliable.  The  kidneys  also  perform  an  important 
office  in  the  work  of  purifying  the  blood.  They  are  a 
pair  of  large  glands,  situated  in  the  upper  and  back 


d 


a.  Cuticle.  6.  Colored  layer  of 
the  skin  (rete  mucosum).  c. 
True  skin,  d,  </.  Perspiratory 
glands.  e,  e.  Perspiratory 
ducts. 


50 


PHYSIOLOGY. 


part  of  the  abdomen,  and  are  concerned  in  separating 
from  the  blood  a  peculiar  substance  called  Urea,  which 
is  formed  in  the  decomposition  of  the  tissues. 


FIG.  23.— OIL  GLANDS. 


a.  Simple  oil  gland.     6.  Oil  glands  surrounding  a  hair. 

Through  these  various  outlets  we  see  what  ample 
provision  is  made  for  purifying  the  blood,  and  remov- 
ing from  the  system  the  waste  matter  resulting  from 
the  tranformation  of  the  tissues.  No  one  of  these  or- 
gans can  suspend  action,  or  be  impaired  in  its  func- 
tions, without  deranging  the  healthy  condition  of  the 
whole  vital  machinery. 

65.  Temperature  Measured  by  the  Air  Breathed.— 

But  a  result  of  respiration,  no  less  curious  than  it  is 
important,  is  that  of  enabling  a  living  body  to  main- 
tain a  nearly  uniform  heat  independent  of  the  tem- 
perature of  the  surrounding  medium.  It  required  many 
years  of  patient  observation,  and  investigation,  to  reach 
the  cause  of  this  wonderful  phenomenon,  and  even  yet 
there  is  much  connected  with  it  that  is  but  imper- 
fectly understood;  enough  however  is  known  to  satisfy 


KESPIKATION.  51 

scientific  men  that,  primarily,  animal  heat  depends  on 
respiration. 

Fishes,  whose  respiration  is  carried  on  by  gills,  ob- 
taining merely  a  portion  of  the  oxygen  which  water 
is  capable  of  absorbing,  have  a  temperature  but  little 
above  that  of  the  water  in  which  they  live.  Reptiles, 
breathing  with  membranous  lungs,  and  inhaling  but 
a  small  volumn  of  air,  and  retaining  but  little  of  its 
oxygen,  are  cold-blooded  animals,  or  nearly  so.  With 
them,  breathing  may  be  suspended  for  an  hour  or 
more,  even  while  the  animal  is  active;  and  when  the 
temperature  of  the  atmosphere  falls  to  near  the  freez- 
ing point,  respiration  is  suspended  entirely  and  indef- 
initely, and  the  reptile  remains  torpid  until  the  tem- 
perature rises  again. 

66.  Mean  Temperature  of  the  Body.  Effect  of 
Evaporation. — Among  warm-blooded  animals  the  tem- 
perature varies  somewhat,  but  is  always  measured  by 
the  amount  of  oxygen  consumed.  In  man,  the  tem- 
perature, in  health,  varies  but  little  from  ninety-eight 
degrees  Fahr. ;  in  many  of  the  inferior  animals  it  falls 
below  this;  while  in  birds,  it  rises  above  one  hundred 
degrees;  but  birds  breathe  more  air,  in  proportion  to 
their  weight,  than  even  man.  The  actual  amount  of 
air  consumed  in  respiration  is  not  to  be  measured  by 
the  number  of  cubic  feet  of  air  inhaled  in  a  given  time, 
as  the  volume  of  all  gasses  is  materially  increased  by 
an  elevation  of  temperature. 

A  person,  breathing  an  atmosphere  at  zero,  will 
inhale  a  much  greater  quantity  of  air  in  the  same 
volume  than  he  will  with  the  temperature  at  eighty 
degrees.  This  important  provision  materially  aids  in 


52  PHYSIOLOGY. 

maintaining  the  heat  of  the  body  in  cold  climates.  The 
increased  quantity  of  food  required  in  the  winter  season, 
as  well  as  the  kind  of  food  which  the  appetite  de- 
mands, is  a  wise  provision  for  accomplishing  the  same 
purpose. 

To  modify  the  effects  of  a  high  temperature,  the 
perspiratory  function  of  the  skin  is  the  chief  agent. 
Evaporation  is  a  cooling  process;  when,  therefore,  the 
heat  of  the  air  approaches  the  natural  temperature  of 
the  body,  a  copious  evaporation  from  the  skin  relieves 
the  heat. 

Recapitulation. 

Respiration  furnishes  the  blood  with  oxygen,  and  carries  off 
impurities;  these  changes  are  the  source  of  animal  heat. 

Secretion  is  performed  by  glands.  The  liver  secretes  bile.  The 
cutaneous  surface,  prespiration.  Oil  glands.  The  kidneys  sep- 
arate urea  from  the  blood. 

Animal  heat  depends  on  respiration.  Normal  temperature  of 
the  human  body  is  ninety-eight  degrees,  and  is  uniform  in  dif- 
ferent climates. 


LESSON    IX. 

GROWTH   AND    REPAIR. 

67.  Growth  and  Repair — why  complex. — The  im- 
mediate action  of  nutrition,  that  is,  the  original  growth 
of  all  the  parts  of  the  body,  and  the  repair  of  the 
constant  waste  which  is  the  necessary  result  of  every 
motion  in  the  animal  machine,  is  a  very  complicated 
process,  and  there  is  much  about  it  which  is  but  im- 
perfectly understood;  much  which  the  human  mind 


GROWTH   AND  REPAIR.  53 

may  never  fully  comprehend.  What  is  done,  we  know; 
and  the  general  laws  under  which  the  great  work  of 
growth  and  of  repair  is  carried  on,  are  understood  in 
the  main  points  relating  to  their  practical  application. 
From  the  very  nature  of  the  chemical  and  vital  forces 
involved  in  this  work,  there  must  remain  much  that  is 
unknown,  perhaps  unknowable. 

68.  Composition  of  the  Blood. — All  the  tissues  of 
the    body,   from    the    tender   and   delicately  organized 
brain  to  the  most  compact  and  solid  bone,  are  formed 
from  material  taken  into  the  body  as  food,  digested  in 
the  stomach,  dissolved  in  the  blood,  and  from  that  fluid 
separated  and  built  into  its  proper  place,  while  that 
fluid    is    being    transmitted    through    the    capillaries. 
Healthy  blood,  on  cooling,  separates   into  a  semi-solid 
substance   called  Coagulum,  and  a   nearly  transparent 
fluid,  the  Serum.     This  serum  is  the  basis  of  the  blood, 
and  may  be  considered  as  water,  holding  the  coagulum 
and  several  mineral  substances  in  solution. 

In  every  one  hundred  parts  of  blood,  there  are 
seventy-nine  parts  water,  and  twenty-one  parts  of 
dry  solids.  These  solids  are  dissolved  in  the  serum, 
and  held  in  that  condition  by  the  living  state  of  the 
blood,  and  its  constant  motion.  If  the  blood  be  drawn 
into  a  basin,  though  it  be  kept  at  the  natural  tem- 
perature of  the  body,  yet  it  rapidly  separates  into 
coagulum  and  serum. 

69.  Proportion  of  the  Ingredients  in  the  Blood.— 

The  coagulum,  if  carefully  washed  in  cold  water,  may  be 
reduced  to  a  white  fibrous  mass,  much  like  muscles 
in  composition  and  appearance.  The  matter  which  has 
been  washed  out  is  found  to  consist  of  a  coloring  sub- 


54  PHYSIOLOGY. 

stance    rich   in   iron,   from   the   oxide   of   which    metal 
it  has  been   supposed  to  derive    its   color.    . 

Of  the  twenty-one  parts,  in  one  hundred,  of  solid 
matter  contained  in  healthy  blood,  about  one-seventh 
is  composed  of  saline  matter,  (chiefly  common  salt,) 
of  fatty  substance,  and  sugar;  two-sevenths  consist 
of  albumen,  a  substance  like  the  white  of  an  egg; 
and  the  remaining  four-sevenths  appear  to  be  derived 
from  the  breaking  down  of  minute  disks,  which  the 
microscope  reveals  in  great  numbers  in  the  blood. 

FIG.  21.— BLOOD  DISKS. 


a.  Colored  disks— various  forms.     6.  Colorless  disks— different 
appearances. 

70.  Blood  Disks  —  two  kinds. —  Of  these  disks,  or 
corpuscles,  as  they  are  sometimes  called,  two  kinds  are 
observed  in  the  blood  of  all  animals  which  suckle 
their  young,  colored  corpuscles  and  colorless  ones.  The 
colored  corpuscles  seen  in  the  human  blood,  are  small, 
circular  bodies,  flattened  into  thin  plates  or  disks. 
The  colorless  corpuscles  are  more  globular  in  form, 
and  vary  in  number  with  the  changing  condition  of 
the  system. 

While  the  colored  corpuscles  appear  to  be  a  constit- 
uent part  of  the  blood  itself,  those  without  color  seem 
in  some  way  intimately  connected  with  the  appropri- 
ation of  nutriment  to  the  growth  and  repair  of  the 
various  organs. 


GROWTH  AND  KEPAIK.  55 

71.  Cell  Structure  of  the  Tissues.— Among  the  as- 
tonishing revelations  of  the  microscope,  none  is  more 
marvelous  than  the  truth  that  all  living  forms,  animal 
and  vegetable,  are,  in    their    ultimate    structure,  com- 
posed of  cells.     These  cells,  in  their  original  form,  are 
globular,  or  slightly  elliptical,  but  when  they  are  built 
into  tissues,  the   pressure  of  the   adjoining  cells  gives 
them  a  great  variety  of  forms.     Sometimes  they  adhere 
together  like   strings  of  beads,  and  form   fibers,  as   in 
the  muscular  tissue;    sometimes  the  cell-walls  are  ab- 
sorbed  at   the   point  of  adhesion,   and   thus   the    fiber 
becomes  a  tube,  as  in  the  white  matter  of  the  brain; 
and  again,  the   globular  cell  will  assume   strange  and 
irregular   forms,   as    seen   in   the   gray   matter  of   the 
brain. 

72.  Cells — how  formed  and  removed. — All  the  vari- 
ous tissues  of  the  body  are  thus  formed,  and  the  original 
cells  appear  very  much   alike.      They   resemble    little 
bladders  or  sacs,  filled  with  a  transparent  fluid;  but  the 
cell-walls  permit  both  fluids  and   gases  to  pass  in  and 
out  of  the  cell  readily,  and  by  this  means  the  cell  be- 
comes filled  with  the  proper  material  to  form  the  differ- 
ent tissues  of  the  body.    Thus  earthy  matter,  filling  cells, 
forms  solid  bone;  fibrine,  in  a  like  manner,  forms  muscle; 
and,  in  like  manner,  all  the  other  tissues  are  formed. 

In  the  waste  and  repair  of  the  tissues,  the  work  on 
both  sides  proceeds  by  cells.  In  the  activities  of  the 
system,  the  cells,  one  by  one,  are  broken  down,  the 
material  of  which  they  were  formed  is  taken  up  by 
the  absorbents  and  conveyed  to  the  proper  organs  to  be 
disposed  of,  and  instantly  the  place  of  each  removed 
cell  is  occupied  by  a  new  and  more  vigorous  one. 


56  PHYSIOLOGY. 

73.  Modes  of  Cell  Growth. — These  cells,  whether  pro- 
duced  in  the  fluids  of   the  body,  or  in  more   intimate 
connection  with   the  tissues,  are  always  produced  from 
a  pre-existent  cell.     In  the  production  of  cells  in  veget- 
able growth,  we  have  been  able  to  examine  the  process 
much  more   clearly  than  is  possible  in  the  animal  tis- 
sues.    Here   we    learn   that   they   multiply   in   several 
ways.     An  existing   cell   may  become    lengthened,  and 
growing   narrow  in   the  middle,  may  assume  the  hour- 
glass  form,   and   finally  separate    into   a   pair   of    inde- 
pendent  cells;    or   cells   may  sprout  from   the  opposite 
points  of  an  existing  cell,  as  from  the  poles  of  a  globe, 
and,   having    attained    their   growth,    disengage    them- 
selves from  the  parent  cell. 

In  whatever  way  cells  may  be  multiplied  or  produced, 
no  well-established  instance  of  the  production  of  a  cell 
without  direct  connection  with  a  pre-existing  one  has 
been  placed  on  record. 

74.  Life  Force — its  relation  to  Cell  Destruction. — 

The  transformation  of  the  tissues  by  the  removal  of  old 
cells,  and  the  formation  and  deposition  of  new  ones  to 
supply  their  place,  appears  to  be,  in  some  way,  inti- 
mately connected  with  the  production  and  expenditure 
of  force  in  the  animal  economy.  Every  movement  of 
the  body  is  accompanied  with  a  correspondent  waste 
of  cells,  and  a  proportional  expenditure  of  force.  We 
live  by  the  death  and  renewal,  one  by  one,  of  the 
cells  composing  the  living  machinery;  and  that  ma- 
chinery is  kept  in  working  order  only  by  being  con- 
stantly renewed.  To  impair  or  disturb  this  destruction 
and  renewal  of  the  cell  structure,  is  to  produce  disease, 
and  to  arrest  it,  is  death. 


GROWTH   AND   REPAIR.  57 

75.  The  Blood  the  Agent  of  Cell  Transformation.— 

The  blood  is  the  immediate  instrument  of  this  vital 
action.  It  conveys  the  prepared  material  for  the  new 
cells  to  the  tissues  where  it  is  to  be  used,  and  removes 
the  remains  of  the  decomposed  cells;  and  as  these 
changes  must  be  constant  and  unintermittent,  that 
life  may  be  maintained,  so  the  blood  must  be  kept 
in  constant  and  incessant  motion,  that  the  cell  trans- 
formation may  not  be  interrupted.  The  pulsation  of 
the  arteries,  measuring  the  circulation  of  the  blood, 
becomes  the  most  important  index  of  t'  nner  in 

which   the   life   functions  are  being  cai  at  any 

given   time. 

76.  Quantity  of  Blood.— The  qu  cir- 
culating in  the  body  is  constantly  in 
the  same  individual;   and  in  differf  ^s 
with  age,  state  of  health,  habits  '  > 
food,  exercise,  etc.     As  a  genera] 

to  estimate  the   quantity  of  bio- 
of  the  weight  of  the  body.     It 
to  the   tissues  will   depend  n 
and   this  will,  to  a   great   exteu  r  oe 
quality  of  food,  and  its  perfect  digest 

Recapitulation 

Growth  and  repair  are  complex,   and 

All  parts  of  the  body  are  repaired  from  t  .d 

substance  of   healthy  blood.     Blood  disks 

All  animal  and  vegetable  structures  ar  .s  of 

various  forms.    Formation  and  removal  <-  their 

growth.     Relation  of  Hie  death  and  rent.\al  01  ^       .       ie. 

Cells  are  built  by  the  blood.     The  blood   constitutes  about 
one-tenth  the  weight  of  the  body. 


58 


PHYSIOLOGY. 


LESSON    X. 

SYSTEM   OF    VOLUNTARY   MOTION. 

\77.  Bones— their  use— how  formed.— Having  briefly 
considered  the  system  of  nutrition,  in  the  several 
functions  which  contribute  to  carry  on  that  work, 


FlG.  25.->-FRONT  VIEW  OF  THK 
SKELETON. 


FIG.  26, 


VIEW  OF  THE 
1TON. 


we  proceed  to  look  at  the  system  of  voluntary  motion. 
This  consists  of  a  number  of  Bones,  so  formed  as  to 


\ 


SYSTEM  OF  VOLUNTARY  MOTION.  59 

serve  as  solid  levers  of  motion,  or  to  act  as  a  protec- 
tion from  injury  to  the  important  and  more  delicate 
organs  of  the  body. 

These  bones  are  originally  formed  of  an  elastic,  semi- 
solid  substance  called  Cartilage.  The  earthy  matter  is 
afterward  deposited  in  it,  so  as  to  give  to  bone  the 
density  and  general  character  of  a  mineral  substance. 
This  process  of  changing  cartilage  to  bone  is  called 
ossification.  In  the  long  bones,  such  as  those  of  the 
limbs,  ossification  begins  near  the  middle,  and  extends 
gradually  toward -the  extremities,  leaving  a  portion  of 
the  extreme  end  of  the  bone,  which,  except  in  very 
old  persons,  still  remain  cartilaginous. 

78.  Composition  of  Bone. — The  proportion  of  animal 
and  earthy  matter  varies  with  the  age  of  the  person, 
with  the  diet,  habits  of  life,  etc.     In   childhood,  the 
earthy  matter  forms  about  one-half  the  weight  of  the 
bone;    in    adult   life,  four-fifths;    and    in   extreme    old 
age,  as  much  as  nine-tenths.     The  hardness  and  brit- 
tleness  of  bone  depends   on  the  proportion  of  earthy 
matter.     And  hence  the  bones  of  old  persons  are  easily 
fractured,  and  unite  slowly  when  broken;  on  the  other 
hand,  the  bones  of  children  are  readily  bent  or  distorted 
by  confinement  in  improper  positions. 

The  earthy  matter  of  bone  consists  almost  entirely 
of  lime,  in  combination  with  phosphoric  and  carbonic 
acids,  and,  like  every  other  part  •  of  the  living  body, 
is  subject  to  the  general  law  of  removal  and  replace- 
ment; but  the  transformation  goes  on  more  slowly  in 
the  bones 'than  in  the  .softer  tissues  of  the  body. 

79.  Structure  of  Bones. — Bones  are  covered  with  a 
dense  fibrous  membrane,  called  the   Periosteum,  from 


60  PHYSIOLOGY. 

which  they  are  supplied  with  nutritive  vessels.  In 
the  long  bones,  the  center  of  the  bone  is  hollowed 
out,  leaving  a  cavity  which  is  filled  with  fatty 
matter  called  marrow.  This  marrow  cavity  does  not 
extend  entirely  to  the  ends  of  the  shaft,  but  its 
place  is  supplied  by  a  porous  structure,  which  not 
only  fills  the  cavity,  but  expands  the  extremity  of 
the  bone,  so  as  to  furnish  a  greater  bearing  surface 
at  the  joints.  The  flat  bones,  such  as  those  of  the 

head,  are  composed  of  two  plates  of  solid, 
FIG.  27.— STRUC-  ,  .     ,  ,.    , 

osseous  matter,  and  an  intermediate  space 

TUxvE    Olf    THE  '  A 

BONES,    filled  with  a  cellular,  bony  structure. . 

80.  Mechanism  of  the  Long  Bones.  — 

Principles  well  known  to  mechanical  phi- 
losophers are  involved  in  this  arrangement 
of  bone  material.  Lightness  is  of  great 
importance  in  a  moving  limb;  but,  at  the 
same  time,  strength  must  be  provided  for 
in  bones  intended  to  sustain  the  weight 
of  the  body,  and  to  afford  attachment  to 
powerful  muscles  which  are  to  be  the  in- 
struments of  complicated,  vigorous,  and 
rapid  motions.  In  no  other  way  could 
both  these  objects  be  secured  so  effectually, 

«,  c.  Spongy  ex-  .  ,,  ,      ,,  .  , 

tremitiesofthe  as    "?   making   the    shafts   of   the    bones 

femur.  hollow. 

>.  Marrow  cav- 
ity in  the  shaft. 


6.  Marrow  cav-  ft    firm     articulation     requireS    that 


the  surfaces  of  the  bones  which  bear  on 
each  other  at  the  joints,  should  be  broader  than  that 
which  a  cross  section  of  the  bone  in  the  middle  of 
the  shaft  would  give.  The  spongy  texture  of  the 
bones  at  their  articulating  ends,  as  seen  in  the  long 


SYSTEM  OF  VOLUNTARY   MOTION.  61 

bones  of  the  limbs,  admirably  accomplish  this  purpose, 
without  increasing  the  weight  or  diminishing  the 
strength. 

81.  Bones  not  Sensitiye.  —  In   a   healthy  condition, 
bones   have    no    sensibility.     When   they   become   dis- 
eased, however,  they  are  often  acutely  sensitive.    The 
popular  idea,  that  the  marrow  of  a  bone  is  very  painful 
when  touched,  is  altogether  false.     Marrow  is  simply  fat 
deposited  in  the  cavities  of  a  spongy  tissue.     It  receives 
nutriment   by  means  of  blood-vessels,   which   pass  ob- 
liquely through  the  walls  of  the  cavity  at  particular 
points,  usually  near  the  middle  of  the  shaft. 

82.  Articulations.  —  Bones   are    joined   together  by 
three    kinds    of   union,    to    wit:    joints,    sutures,    and 
symphyses.     A  Joint  is  the  Ainion  of  two  bones,  admit- 
ting of   motion   at   the   point  of   union.      In  the  true 
joints,  the  ends  of  the  bones  are  covered  with  a  pad,  or 
cushion  of  cartilage,  which  readily  yields  to  pressure, 
and  thus  serves~4o  break  the  concussion  when  the  bones 
composing  the  joint  are  violently •  foj^|jj^ether,  as  in 
jumping  or  running. 

In  youth,  this  cartilage  is  thick;  bu^»h£<>  advances, 
ossification  extends  further  toward  the  exlifefcy  of  the 
bones;  and  in  old  persons,  the  cartilages  of  the  joftt* 
are  nearly  obliterated.  From  this  cause,  old  persons 
are  cautious  in  all  their  movements,  and  carefully  avoid 
leaping,  or  any  other  movement  that  might  bring  the 
ends  of  the  bones  violently  together. 

83.  Ligaments— their  form  and  nse.— The  bones 
uniting  with   each  other  in   joints,  have  the   surfaces 
which   come  together  formed  so  as  to  fit  very  nicely, 
and  they  are  held  in  place  by  bands  of  dense,  fibrous 


62  PHYSIOLOGY. 

substance,   so  arranged  as  to  admit  of  motion  within 
a  limited  range. 

In  the  principal  joints  these  bands,  or  ligaments,  as 
they  are  called,  are  so  connected  as  to  form  a  continuous 
layer,  completely  surrounding  the  articulating  extremi- 
ties of  the  bones,  and  thus  inclosing  the  joint  in  a  kind 
of  sac.  This  continuous  band  is  called  the  Capsular  lig- 
ament. The  articulating  surfaces  of  the  bones,  as  well 
as  the  inner  surface  of  the  capsular  ligament,  is  covered 
with  a  very  fine,  smooth  membrane,  from  which  is 
secreted  a  slimy  fluid,  that  serves  to  lubricate  the 
joint  and  prevent  friction.  This  is  the  synovial  fluid, 
commonly  called  "joint  water." 

84.  Kinds  of  Joints. — There  are  several   forms  of 
joints ;    the    most    important,    however,    are    the    ball 
and   socket    and  the    hinge  joint.     The    first   of  these 
admits  of  motion  in  all  directions,   and  is  well   illus- 
trated in  the  hip  joint.     In  many  respects,  this  is  the 
most    perfect   articulation    in   the   body.      It   allows    a 
greater  range   of  motion  than  any  other ;  has  a  deeper 
socket  and  a  more  perfect  ball  than  is  found  elsewhere ; 
and  it  has,  in  addition  to  a  most  perfect  capsular  liga- 
ment, a  strong  cord  binding  the  extremity  of  the  ball 
to  the  bottom  of  the  socket,  thus  securing  a  wide  range 
of   motion    in   all   directions,   and,   at   the    same   time, 
giving   great  strength  to  the   parts.     The   hinge  joint 
is  well  illustrated   in  the  knee  and  elbow.     It  admits 
of  motion   but   in  one   direction,  or,   rather,   backward 
and  forward  on  the  same  line. 

85.  Irregular  Joints. — At  the  wrist  and  ankle  we 
have  examples  of  compound  joints,  formed  by  the  artic- 
ulation of  a  number  of  bones,  so  adjusted  as  to  allow  but 


SKELETON.  63 

little  motion  between  any  two  bones,  and  yet  the  aggre- 
gate gives  considerable  motion  in  every  direction.  In 
the  spinal  column,  or  back-bone,  we  have  still  another 
contrivance  for  allowing  motions,  though  there  are  no 
articulating  surfaces  between  the  several  pieces  of  the 
column.  An  elastic  cartilage  is  interposed  between 
these  pieces,  adhering  firmly  to  each,  and  thus,  by 
compression  and  distention,  furnishing  a  good  degree 
of  motion.  Nearly  akin  to  this'  is  that  kind  of  union 
between  bones,  called  Symphysis,  where  two  bones  are 
joined  by  smooth  edges,  and  held  in  place  by  a  thin 
layer  of  cartilage  interposed.  This  kind  of  union  does 
not  admit  of  motion.  If  the  edges  are  indented,  or 
dove-tailed  into  one  another,  and  the  cartilage  omitted, 
the  union  is  called  a  Suture. 

Recapitulation. 

Bones  are  formed  from  cartilage.  Earthy  matter  forms  from 
one-half  to  nine-tenths  of  the  bones.  They  are  covered  by  the 
periosteum,  and  contain  marrow  in  central  cavity.  Form  of  bone 
best  for  strength  and  lightness.  Bones  are  not  sensitive.  They 
are  united  by  joints,  sutures,  and  symphyses.  Form  and  use  of 
ligaments.  Synovial  fluid  prevents  friction.  Varieties  of  joints, 
ball  and  socket,  and  hinge.  Irregular  forms.  Symphysis  and 
suture  denned. 


LESSON    XI. 

SKELETON. 

86.  The  Skeleton — its  division.  —  The  bones  of  the 
body,  arranged  in  their  natural   position,  constitute  a 

Skeleton.     When  the  bones  are  held  together  by  the 
B.  P.-G. 


64 


PHYSIOLOGY. 


ligaments,  the  group  is  called  a  natural  skeleton;  if 
these  have  been  removed,  and  the  bones  are  held  in 
place  by  means  of  wires,  it  is  an  artificial  skeleton. 

Anatomists  usually  enumerate  two  hundred  and  eight 
bones  in  the  skeleton,  not  including  the  teeth.  Some, 
however,  reckon  more,  others  less  than  this  number,  for 
reasons  which  will  appear  in  the  further  description 
of  the  particular  bones.  For  convenience  of  description, 
the  skeleton  is  divided  into  four  sections :  1st.  Bones 
of  the  head;  2d.  Bones  of  the  trunk;  3d.  Bones  of  the 
upper  extremities;  4th.  Bones  of  the  lower  extrem- 
ities. 

87.  Bones  of  the  Head.  —  The  Head  is  divided  into 
bones  of  the  skull  and  of  the  face.  The  Skull,  or  cra- 
nium is  composed  of  eight  bones.  The  frontal  bone 

FIG.  28.— FUONT  VIEW  OF  SKULL.  FIG.  29.— BASE  OF  THE  SKULL. 

m^^ c^ 

& 


.  Frontal  bone.  b.  Right  parietal 
bone.  c.  Left  parietal  bone.  il. 
Left  temporal  bone. 


a.  Foramen  magnum. 
6.  Occipital  bone. 
c,  c.  Zygomatic  arch. 


occupies  the  region  of  the  forehead.  The  side  of  the 
head  has  a  pair  of  parietal  bones  in  the  upper  region, 
and  a  pair  of  temporal  bones  below.  The  back  part  of 


SKELETON. 


FIG.  30.— VEKTICAL  VIEW  OF  THE 
SKULL. 


the  head,  and  most  of  the  base  of  the  skull,  is  occupied 
by  the  occipital  bone.  In  the  forward  part  of  the  base 
of  the  skull  are  two  small  bones,  the  ethmoid  and  sphenoid, 
which  are  seen  only  by  removing  the  upper  part  of  the 
skull. 

88.  The  Cranial  Arch— Bones  of  the  Face.— The 

bones  of  the  skull  are  joined  firmly  by  sutures,  and  the 
shape  of  each  bone  is  such  as  to  present  the  form  of  an 
arch  in  whatever  line  it  is 
measured;   and  the   whole 
skull    forms    a    dome,    or 
arched  roof  of  the  chamber 
where  the  brain,  the  most 
important    organ    of    the 
body,    is    carefully    depos- 
ited. 

The  bones  of  the  skull 
are  made  of  two  plates, 
separated  by  a  thin  layer 
of  spongy  bone.  By  this 
arrangement  the  concus- 
sion, or  jar  of  injuries  re- 
ceived on  the  outer  plate, 
is  mainly  arrested  before 
it  reaches  the  brain.  The 
bones  near  the  base  of  the 
skull  are  much  thicker  than  those  which  form  its  sides 
and  upper  part.  This  serves  as  a  solid  abutment  to  the 
arch,  to  enable  it  to  withstand  severe  blows  on  the  top 
of  the  head,  or  to  resist  great  pressure  at  that  point. 
The  Face  is  composed  of  fourteen  bones. 


b 


d- 


a.  Frontal  bone.  6,  6.  Parietal 
bones,  c.  Occipital  bone.  <7,  <1. 
Lambdoidal  suture,  e,  e.  Coronal 
suture.  /.  Sagittal  suture. 


89.  The  Spinal  Column.  — The  trunk  is  divided  into 


66 


PHYSIOLOGY 


FIG.  31. 
SPINAL,  COLUMN. 


Cervical 
Vertebrae. 


the  thorax  and  the  pelvis.     These,  with  the  soft  parts 
connected,  form  two  important  cavities  —  the  chest  and 
the  abdomen.     The  thorax  consists 
of  the  spinal  column,  the  ribs,  and 
the  sternum,  or  breast-bone. 

The  Spinal  column  consists  of 
twenty-four  bones.  Each  bone  is 
called  a  Vertebra.  Seven  of  these 
are  in  the  neck  (cervical  vertebrae), 
twelve  in  the  back  (dorsal  verte- 
brae), and  five  in  the  loins  (lumbar 
vertebra).  Each  vertebra  consists 
of  a  body  and  seven  projecting 
bones,  called  processes.  These  pro- 
cesses unite  at  their  base,  so  as  to 
form  a  continuous  tube  for  the 
passage  of  the  spinal  cord.  This 
tube  does  not  pass  through  the 
body  of  the  vertebra,  but  lies  just 
back  of  it. 


Sacrum. 


90.  Union  of  the  Yertebrae.  —  The  vertebrae  are 
united  together  by  a  -layer  of  cartilage  which  is 
firmly  attached  to  each  bone,  and  yet  it  has  elasticity 
enough  to  admit  of  considerable  motion ;  but  the  broad 
and  strong  band  of  ligaments  which  binds  the  articu- 
lating processes  together,  limits  that  motion,  and  renders 
the  articulation  more  firm  and  secure  than  any  other 
joint  in  the  body. 

The  spinal  column,  when  viewed  from  the  back, 
should  present  a  straight  line;  but  viewed  laterally, 
it  is  slightly  curved  like  the  letter  S.  This  form  is  a 
wise  arrangement,  serving  to  break  the  force  of  any 


SKELETON. 


67 


sudden  jar  of  the  body,  and  thus  save  the  brain  from 
the  concussion. 


FIG.  32.— A  LUMBAR  VERTEBRA. 


FIG.  33.— THE  THORAX. 


a.  Body  of  the  vertebra.     6,  6.  Transverse  processes,     c,  c.  Articulating 
processes,    d.  Spinous  process. 

91.  The  Ribs— their  articulation.  —  The  Ribs  form 
the  side  walls  of  the 
thorax.  They  are  twen- 
ty-four in  number  — 
twelve  on  each  side  — 
and  are  divided  into 
three  classes.  Seven  are 
true  ribs,  three  are  false 
ribs,  and  two  are  float- 
ing ribs.  Each  rib  has 
two  curvatures  —  one 
which  bends  it  around 
the  chest  horizontally, 
and  another  which  gives 
it  a  downward  curva- 
ture from  the  back  for- 
ward. 

The  ribs  are  united 
to  the  vertebra  by  true 
joints,  but  forward,  the  true  ribs  join  the  breast-bone 


a.  Sternum.  6.  Seven  true  ribs.  c. 
Three  false  ribs.  rf.  Two  floatiug 
ribs.  e.  Dorsal  portion  of  the  spinal 
column. 


PHYSIOLOGY. 


FIG.  34.— THK  PKT.VIS. 
a 


by  flexible  cartilages.  The  three  false  ribs  unite  to  a 
cartilage  which  is  common  to  all  of  them,  and  by 
means  of  which  they  are  attached  to  the  breast-bone. 
The  floating  ribs  ha\ve  no  forward  attachment. 

92.  The  Sternum.  Bones  of  the  Pelvis.  — The  Ster- 
num, or  breast-bone, 
forms  the  front  of  the 
thorax.  In  infancy, 
it  is  in  eight  distinct 
pieces ;  in  youth, 
three ;  and  in  old  age, 
but  one.  It  is  the 
last  bone  in  the  body 
to  ossify,  and,  except 
in  extreme  old  age, 
the  point  at  the  lower 
end  remains  cartilagi- 
nous. 

The  Pelvis,  or  lower 

division  of  the  trunk,  consists  of  four  bones.  The 
Sacrum,  which  forms  the  back  part  of  the  basin,  appears 
like  a  continuation  of  the  spinal  column,  only  that  the 
vertebra  are  grown  firmly  together.  At  the  extreme 
lower  point  of  the  sacrum  is  a  small  conical  bone,  called 
the  Coccyx.  On  each  side  of  the  sacrum,  and  uniting 
with  each  other  in  front,  is  a  large,  irregular  formed 
bone,  called  the  Innominatum.  In  early  life  this  is  com- 
posed of  three  pieces,  and  it  is  often  described  as  three 
distinct  bones;  but  in  adults  they  become  completely 
united. 

93.  Shoulder,    Arm,    Forearm,    and    Hand.  —  The 

upper  extremity  is  divided  into  the  shoulder,  arm,  fore- 


a.  Sacrum.     6,  6.  Right  ami  left  innom 
inatutn.    c.  Coccyx. 


SKELETON. 


FIG.  35.— LEFT  CLAVICI.K. 


a.  Articulation  with  the  acroraion  pro- 
cess of  the  scapula.  6.  Articulation 
with  the  sternum. 


FIG.  36 


arm,  and  hand.   The  shoulder  consists  of  a  large,  triangu- 
lar bone,  the  Scapula, 
or  shoulder-blade,  and 
the  Clavicle,  or  collar- 
bone,    which     is    at- 

•  ^^^^^fc^^^^*" 

tached    to   the    upper 

end  of  the  sternum  at 

one  extremity,  and  to 

the  scapula  at  the  other. 

The  arm  has  one  bone,  the  Humerus,  which  is  articu- 
lated, by  a  ball  and 
socket  joint,  to  the 
head  of  the  scapula 
above,  and  to  the 
bones  of  the  forearm 
by  a  hinge  joint  be- 
low. The  forearm 
consists  of  two  bones, 
the  Radius  on  the 
side  of  the  arm  cor- 
responding to  the 
thumb,  and  the  Ulna 
on  the  other  ^side. 
The  ulna  forms  the 
principal  part  of  the 
elbow  joint,  but  the 
radius  gives  the 
chief  articulation  at 
the  wrist. 

Three  groups  of 
bones  form  the 
hand.  The  Carpus, 

or  wrist,  consists   of   eight  bones;   the   Metacarpus,  or 


ft.  /icromion  process.  6.  Coracoid  process. 
o.  Spine,  or  ridge  on  the  back  of  the  scap- 
ula, d.  Articulation  of  the  huraerus. 


70 


PHYSIOLOGY. 


palm  of  the  hand,  has  five  bones ;  and  the  fingers  have 
three  -bones,  or  phalanges,  in  each ;  while  the  thumb 
has  but  two. 


FIG.  37. 
HUM  EU  us. 


FIG.  38.— ULNA 
AND  RADIUS. 


FIG.  39.— CAUPUS  OR 
WRIST. 


a.  Shoulder  artic- 
ulation. 

6.  Elbow  articula- 
tion. 


a.  Elbow  articula- 
tion. 

6.  Wrist  articula- 
tion. 


a.   Carpus   or  wrist— eight 
bones.  6.  Metacarpal  bones. 

c.  Lower  end  of  the  Radius. 

d.  The  ulna. 


94.  Bones  of  the  Lower  Extremities.  —  The  lower 
extremity  is  divided  into  the  thigh,  leg,  and  foot.  The 
Femur,  or  bone  of  the  thigh,  is  the  largest  long  bone  of 
the  body.  At  the  upper  end  it  has  a  head,  which 
stands  at  an  angle  of  about  forty-five  degrees  with  the 
shaft  of  the  bone.  This  head  is  received  into  a  deep 
cavity  in  the  innominatum,  and  forms  a  complete  ball 
and  socket  joint.  The  bones  of  the  leg  are  the  Tibia 
which  articulates  with  the  femur  by  a  hinge  joint;  the 
Fibula,  a  small  bone  placed  on  the  outer  side  of  the  tibia 
as  a  kind  of  brace ;  and  the  Patella,  or  knee-pan,  a  flat, 
oval-shaped  bone,  placed  on  the  front  of  the  knee  joint 


SKELETON. 


71 


to  serve  as  a  kind  of  pulley.     The  foot  consists  of  the 
Tarsus,  or  ankle,  a  group  of  seven  bones;  the  Metatarsus, 


FJG.  41.— TIBIA  AND 
FIBULA. 


a 


«.  Head  of  the  femur. 
6.  Articulating  sur- 
face at  knee  joint. 


a.  Tibia.  6.  Fibula. 
c.  Knee  joint.  d. 
Ankle  joint. 


FIG.  42.— TAKSUS  AND 
MKTATARSUS 


a 


a.  Seven  tarsal  bones. 
6.  Five  metatarsal 
bones. 


or  foot  proper,  with  five  bones  and  the  toes,  with  three 
bones  in  each,  save  that  the  great  toe  has  but  two. 
Small  bones,  called  Sesamoid  bones,  which  are  not  enu- 
merated here,  are  frequently  found  near  the  joints. 

Recapitulation. 

Skeleton,  natural  or  artificial,  consists  of  two  hundred  and 
eight  bones.  The  skull  consists  of  eight  bones  joined  by  sut- 
ures, and  consisting  of  two  plates  separated  by  spongy  matter. 
The  face  is  composed  of  fourteen  bones. 

The  thorax  consists  of  spinal  column,  ribs  and  sternum.  The 
spinal  column  consists  of  twenty-four  bones  united  by  layers  of 
B.  P.— 7. 


72  PHYSIOLOGY. 

cartilage.    There  are  twenty-four  ribs,  all  jointed  to  the  spinal 
column,  ten  on  each  side  joined  to  the  sternum. 

The  sternum  consists  of  from  one  to  eight  bones.  The  pelvis 
consists  of  four  bones.  The  upper  extremities  consist  of  thirty- 
two  bones  each,  the  lower  of  thirty  each. 


LESSON   XII. 

MUSCLES. 

95.  Muscles  and  their  functions. — The  bones,  with 
their  joints  held  firmly  together  by  ligaments,  and  yet 
permitting  much  freedom  of  motion,  are  admirably 
adapted  to  the  great  variety  of  movements  required 
to  perform  all  the  functions  of  the  human  body.  But 
the  bones  have  no  power  of  motion;  they  are  merely 
the  machinery  of  motion,  to  be  operated  on  directly  by 

the   muscles,    and   remotely 
FIG.  43.— MUSCULAR  FIBERS  AS     ,       ,, 

SEEN  BY  A  MICBOSCOPK.          by  the  nervous  system. 

Muscles  are  formed  of  nu- 
merous bundles  of  fleshy 
fibers,  bound  together  by  a 
firm  membrane,  called  the 
Facia.  The  fibers  of  which 
a  muscle  is  composed  are 

exceedingly  fine  threads ;  and  yet  the  microscope  reveals 
the  fact  that  each  fiber  is  composed  of  a  string  of  cells 
slightly  elliptical  in  form,  and  attached  together  by 
their  longer  axes.  By  changing  the  form  of  these  cells 
so  that  they  become  more  globular  in  shape,  the  fiber  is 
made  shorter;  and  this  change  taking  place  at  the  same 
time  in  all  the  fibers  of  a  muscle,  the  parts  to  which  the 


MUSCLES, 


73 


FIG.  44.— TENDONS  OF 
THE  RIGHT  HAND. 


a 


two  ends  of  the  muscle  are  attached  are  drawn  nearer 
together.     This  is  muscular  contraction. 

96.  Tendons— their  form  and  use.— The  manner 
in  which  the  will  directs,  and  the  extent  it  governs 
this  contraction  and  consequent 
motion,  and  the  part  which  the 
brain  and  nerves  perform  in  this 
work,  will  be  explained  when  we 
come  to  study  the  Nervous  System. 

The  muscles  which  move  the 
limbs,  and  perform  the  chief  vol- 
untary movements,  have  various 
forms,  generally  swelling  larger 
near  the  middle,  and  tapering 
toward  the  end  where  motion  is  ef- 
fected ;  they  usually  terminate  in  a 
dense>  white  cord  called  a  Tendon. 
These  tendons  are  sometimes  very 
long,  as,  for  example:  the  muscles 
which  move  the  hand  are  situated 
on  the  forearm,  just  below  the  elbow, 
and  their  tendons  are  carried  down 
over  the  wrist  joint,  and  inserted 
into  the  bones  of  the  hand  and 
fingers. 


a.  Muscles  which  move 
the  fingers.  6.  Ten- 
dons extending  from 
the  muscles  to  the 
fingers,  c.  Annular 
ligament. 


97.  Union  of  Tendons  with 
Muscles.  —  In  this  manner,  symmetry  and  lightness  ia 
secured  for  the  hand,  while  great  variety  and  force  give 
character  to  its  motions.  So,  in  other  parts  of  the  body, 
the  muscles  are  placed  where  they  will  be  least  in  the 
way,  and  where  they  will  most  conduce  to  symmetry 
and  beauty  of  form ;  and  the  motion  produced  by  their 


74  PHYSIOLOGY. 

contraction  is  conveyed  by  means  of  tendons  to  the 
point  where  it  is  to  have  its  effect. 

The  muscular  and  tendonous  fibers  interlock,  so  that 
it  is  impossible  to  say  precisely  where  the  muscle  ends 
and  the  tendon  begins ;  yet  the  two  kinds  of  fibers  differ 
materially.  The  fibers  forming  the  tendonous  cords  are 
very  fine,  hard,  inelastic,  and  strong ;  and  though  the 
muscles  are  so  much  larger  than  the  tendons,  yet  a 
sufficient  force  applied  will  tear  the  muscle  in  two 
before  the  tendon  will  break.  Where  the  tendons  are 
attached  to  bones,  the  fibers  penetrate  the  solid  bone, 
and  hold  very  firmly. 

98.  Arrangement  of  Muscles  in  producing  Motion. — 

The  broad,  flat  muscles,  such  as  form  the  walls  of  the 
abdomen,  etc.,  commonly  have  a  tendon  on  one  side, 
into  which  the  muscular  fibers  are  inserted;  or  a  ten- 
donous band  passes  through  the  middle,  into  which  the 
fibers  run  obliquely  on  each  side. 

The  most  common  arrangement  for  motion  is  where 
each  end  of  a  muscle  is  inserted  into  a  different  bone, 
and  these  united  by  a  movable  joint.  In  this  arrange- 
ment, the  muscle  is  situated  on  the  fixed  part,  or  that 
which  does  not  move,  and  the  motion  is  conveyed  over 
the  joint  to  the  movable  part  by  means  of  a  tendon. 
There  are,  however,  a  great  diversity  of  arrangements 
in  the  smaller  muscles,  designed  for  the  production 
of  special  and  complicated  motions. 

99.  Bones  as  Levers. — To  understand  the  mechanism 
of  muscular  motion,  we  must  learn  that  bones  are  true 
levers,  having  the  fulcrum,  or  fixed  point  of  the  lever, 
at  the  joint,  the  attachment  of  the  tendon  to  the  bone 
answering  to  what  is  called  the  power,  and  the  extrem- 


MUSCLES.  75 

ity  of  the  limb  or  part  moved  representing  the  weight. 
There  may  be  three  adjustments  of  these  points  in 
every  lever,  and  all  of  these  are  found  in  the  human 
body;  but  that  which  is  commonly  called  the  third 
form  of  the  lever  —  that  which  placesxthe  power  be- 
tween the  fulcrum  and  the  weight  —  is  by  far  the  most 
common  arrangement. 

FIG.  45.— MUSCULAR  MOTION. 


V 

a.  Flexor  muscle  of  the  arm.    6.  Tendon  inserted  into  the  radius, 
c.  Extensor  muscle,    w.  The  resistance. 

100.  Economy  of  Motion. — The  general  principle 
on  which  muscles  are  arranged  is  that  of  producing 
a  great  measure  of  motion  by  a  very  small  amount 
of  contraction.  In  Fig.  45,  the  muscle  which  is  marked 
a  is  fastened  by  its  tendon  to  the  forearm  at  b.  Now, 
if  the  muscle  a  is  made  shorter,  it  will  draw  b  upward 
to  the  extent  of  its  shortening;  but  an  amount  of 
motion  at  b  will  move  the  weight  at  w  as  much  further 
as  the  distance  between  w  and  6  is  greater  than  the 
space  between  b  and  the  center  of  the  joint.  But  this 
will  require  that  the  power  applied  at  b  be  as  much 
greater  than  the  weight  at  w  as  the  space  through 
which  w  is  moved  is  greater  than  that  through  which  b 
passes.  This  is  the  economy  of  motion  at  the  expense 


76  PHYSIOLOGY. 

of  power,  and  may  be  regarded  as  the  general  principle 
of  muscular  motion  in  the  human  body. 

101.  Levers  of  the  second  and  third  classes.  —  In 

reversing  the  motion  of  the  arm,  as  seen  in  the  above 
cut  (Fig.  45),  the  muscle  c  is  attached  by  its  tendon  to 
a  process  of  the  ulna,  which  projects  backward  and 
upward  beyond  the  joint,  and  the  fulcrum  is  placed 
between  the  power  and  the  weight.  But  the  power 
being  applied  to  the  short  end  of  the  lever,  produces, 

by  a  small  motion  there,  a 

MOVEMENT*™  WALKING.         great  motion  at  the  weight 

end  of  the  lever. 

In  the  foot  we  have  the 
other  adjustment,  or  second 
form  of  the  lever,  as  seen  in 
Fig.  46,  where  a  is  the  large 
muscle  on  the  back  of  the 
leg,  which  draws  the  heel 
C/'  upward  when  we  rise  on 

«.  Large   muscle  of  the  leg.     b.      QUr  t  fi  j     th     }  bone 

Tibia,     c.  The  fulcrum. 

of  the   leg,    by  which    the 

weight  of  the  body  rests  upon  the  bones  of  the  ankle 
joint;  c  is  the  fulcrum  or  fixed  point,  on  which  the 
whole  weight  of  the  body  is  raised  in  walking. 

102.  The  Power  of  Muscular  Contraction.— It  will 
be    seen,    from    what    we    have    said,    that    the    power 
exerted   in   the   contraction    of   the    muscles   is   many 
times    greater   than    that    manifested    in   the    motions 
produced.     This  loss  of  power  is  not  merely  the   effect 
of  the   application  of   the   force   to  the   short   arm   of 
the   lever,    but    perhaps    more    is    lost    in    power    and 
gained  in  motion  by  the  direction  in  which  the  force 


MUSCLES.  77 

is  exerted.  This  is  seldom  in  the  line  in  which  the 
motion  is  to  be  obtained,  but  usually  very  obliquely 
to  it;  as,  for  example,  when  a  limb  is  to  be  bent,  as 
the  arm  at  the  elbow  joint,  the  muscles  on  the  upper 
arm  contract,  but  the  tendency  is  chiefly  to  draw  the 
bones  of  the  fore-arm  up  against  the  humerus  at  the 
elbow  joint.  The  tendency  to  bend  the  arm  would  be 
almost  nothing  if  it  were  not  for  a  contrivance  by 
which  the  direction  of  the  tendon,  in  passing  over  the 
joint,  is  changed.  This  is  simply  an  enlargement  of 
the  humerus  at  its  lower  end,  so  that  the  tendon  passes 
over  it  as  over  a  pulley. 

103.  Special  Arrangements  of  Muscles.  Number 
of  Pairs.  —  There  are  many  special  contrivances  for 
producing  peculiar  motions  that  are  noticed  and 
minutely  described  by  anatomists,  but  which  our  pur- 
pose will  not  allow  us  to  even  name.  The  con- 
trivance by  which  the  eyelids  are  closed  in  winking, 
and  that  which  draws  the  lower  jaw  downward  in 
opening  the  mouth,  are  among  the  most  curious  and 
complicated  of  muscular  movements. 

The  muscles  of  voluntary  motion  are  arranged  in 
pairs  on  each  side  of  the  body,  so  that  the  right  and 
left  sides  correspond  exactly  in  the  number  and  posi- 
tion of  their  muscles.  Anatomists  have  named  and  de- 
scribed about  two  hundred  and  forty  pairs  of  voluntary 
muscles,  many  of  these,  however,  are  very  small,  and 
apparently  unimportant. 

Recapitulation. 

Bones  are  moved  by  muscles.  These  consist  of  fibers,  and 
each  fiber  of  cells.  Muscular  contraction  is  effected  by  chang- 
ing the  form  of  cells.  Tendons  are  used  to  attach  muscles  to 


78  PHYSIOLOGY. 

bones,  and  to  transfer  motion.  Muscles  are  not  generally  situ- 
ated on  the  parts  moved  by  their  contraction.  Bones  are  used 
as  levers.  Power  moving  them  arranged  to  economize  motion. 
Muscular  contraction  exerts  a  force  greater  than  that  realized 
through  the  mechanism  of  motion.  Number  of  voluntary 
muscles  —  about  two  hundred  and  forty  pairs. 


LESSON    XIII. 

MUSCULAR   MOTION — VOICE. 

104.  Muscular    Motion  —  voluntary    and    involun- 
tary.— There    are   a  number  of  very  interesting   phe- 
nomena connected  with  muscular  action,  two  or  three 
of  which  will  be  considered  in  this  lesson.     All  animal 
motion,  of  whatever  kind  it  may  be,   is  produced  by 
muscular    contraction.     A    part    of    these    motions    are 
urfder  the  control  of  the  will,  and  are  therefore  called 
voluntary  motions;    another   class  of  motions   are    en- 
tirely independent  of  the  will,  or  even  the  consciousness 
of  the   animal  in  which  the  motion  is  performed,  and 
are  called  involuntary  motions. 

The  organs  thus  controlled  belong  more  directly  to 
the  class  on  which  depend  the  immediate  functions 
of  life.  The  heart  and  stomach  are  each  active  organs, 
but,  in  a  healthy  condition,  we  neither  control  nor 
feel  their  movements.  The  wisdom  of  this  arrange- 
ment is  very  obvious,  for  it  would  be  unsafe  to  trust 
such  important  functions  to  our  voluntary  attention. 

105.  Articulate   Language.  —  Thoughts,   sensations, 
and    emotions    are    communicated    to    others    by   mus- 
cular   motion   only.      In   man   this   communication    is 
made   chiefly  by  means  of  articulate  language,  and  is 


THE  VOICE. 


79 


much  more  extended  and  perfect  than  in  the  lower 
animals,  whose  language  consists  of  a  few  simple 
sounds,  accompanied  by  certain  movements  of  the 
body  which  forcibly  express  a  limited  range  of  thought 
and  passion. 

The  barking  of  a  dog,  the  purring  of  a  cat,  or  the 
clucking  of  a  hen,  each,  taken  with  the  motions  and 
attitudes  of  the  body  accompanying  it,  conveys  mean- 
ing; but  the  thoughts,  however  forcibly  they  may 
impress  us,  are  not  communicated  with  the  clearness 
of  articulate  language.  The  muscles  of  the  human 
face,  which,  by  contracting,  change  the  features  so  as 
to  give  what  is  called  expression 
to  the  countenance,  greatly  assist 
in  making  language  impressive. 


FT      47.— LARYNX— SIDE 
VIEW. 

,e 


—G 


106.  Anatomy  of  the  Larynx.— 

Voice  is  produced  in  an  organ 
called  the  Larynx,  which  is  placed 
on  the  top  of  the  trachea.  It  con- 
sists of  five  cartilages,  arranged  so 
as  to  form  a  most  perfect  musical 
instrument,  which,  by  means  of 
air  passed  through  it  with  more 
or  less  force,  gives  all  the  varied 
tones  of  the  human  voice.  The 
Cricoid  cartilage  is  a  ring,  narrow 
in  front  and  broad  behind,  and  is 
securely  attached  to  the  trachea 
by  its  lower  margin. 
On  the  front  part  of  this,  and  overlapping  it,  is  placed 
the  Thyroid  cartilage;  this  is  attached  to  a  small 
U-shaped  bone,  situated  at  the  root  of  the  tongue,  both 


d- 


«.    Hyoid     bone.      ft. 
Thyroid      cartilage. 

c.  Cricoid  cartilage. 

d.  Trachea,     e.  Epi- 
glottis. 


80 


PHYSIOLOGY. 


by  a  broad  ligament  and  by  muscles  which  move  it 
in  swallowing  food,  in  speaking,  singing,  etc.  The 
thyroid  cartilage  forms  the  projection  on  the  front  of 
the  neck  called  Adam's  Apple,  by  the  motions  of 
which  the  movements  of  the  cartilage  may  be  readily 
observed. 

107.  Yocal  Cords  and  Glottis. — Two  small  triangular 
bodies,  called   the  Arytenoid  cartilages,  are   placed  on 

the   back    part   of  the  cricoid 
no.  48,-Tins  GLOTTIS  AND     cartilage,   and  so  joined  to   it 

VOCAI.  CORDS.  >   '  J 

-,  ,  as    to    admit    of    considerable 

o\  ,-b 

motion  at  the  joint ;  from  these 

are  stretched  two  pairs  of  liga- 
ments called  Vocal  cords,  which 
are  attached  to  the  upper  edge 
of  the  thyroid  cartilage  at  the 
front  part.  The  vocal  cords 
are  formed  of  very  fine  elastic 
fibers,  inclosed  in  a  delicate 
mucous  membrane.  The  space 
between  the  upper  and  lower 

Pilir  °f  COrds  is  Called  the  Ven" 

tricle,  and  the  opening  between 
the  cords  of  each  pair  is  called 
the    glottis.     These   parts   will 
bo  better  seen  in  the  figure   attached. 


«.  Upper  edge  of  the  tnyroid 
cartilage,  b,  b.  Arytenoid 
cartilages,  c,  c.  Vocal  cords. 
il.  Glottis. 


108.  The  Epiglottis.  — The  Epiglottis  is  a  thin,  car- 
tilaginous valve,  which  closes  the  glottis  by  resting 
firmly  on  the  upper  pair  of  vocal  cords,  thus  forming  a 
kind  of  bridge,  by  which  the  food  and  drink  are  con- 
veyed safely  over  the  glottis  into  the  pharynx  and 
oesophagus,  which  lie  back  of  the  air  passage.  If  we 


THE   VOICE.  81 

attempt  to  speak  or  laugh  while  in  the  act  of  swallow- 
ing, the  epiglottis  will  be  raised,  permitting  the  food 
or  drink  to  fall  into  the  trachea,  and  thereby  produce 
strangling. 

In  ordinary,  quiet  breathing,  the  vocal  cords  are 
relaxed,  and  the  epiglottis  thrown  up,  so  as  to  partially 
close  the  passage  into  the  mouth,  and  thus  direct  the 
air  through  the  nasal  passages.  The  upper  pair  of 
vocal  cords  serve  chiefly  as  a  resting  place  for  the 
epiglottis,  and  are  but  little  concerned  otherwise  in 
the  ordinary  production  of  voice. 

109.  The  Pitch  of  Yoiee— its  mechanism.  —  The 
lower  cords  are  exceedingly  delicate,  and  the  edges, 
which  form  the  glottis  proper,  are  very  fine,  and  when 
drawn  tensely,  they  present  an  instrument  of  vibration 
more  perfect  than  any  that  has  been  produced  by  art. 
It  is  a  well  established  principle,  that  the  pitch  of  a 
sound,  produced  by  a  vibrating  cord,  is  determined  by 
its  length,  size,  and  tension. 

Now  the  vocal  cords,  fastened  firmly  at  the  back  to 
the  arytenoid  cartilages,  and  running  obliquely  upward 
and  forward,  are  attached  to  the  front  of  the  thyroid 
cartilage,  and  if  this  be  drawn  upward,  it  will  make 
the  vocal  cords  very  tense.  These,  being  elastic,  dimin- 
ish in  size  as  their  tension  increases. 

We  liave  thus  two  conditions  of  elevated  pitch,  but 
we  have  by  this  movement  lengthened  the  cords  which 
would  have  a  contrary  effect.  To  counteract  this,  the 
arytenoid  cartilages  are  drawn  closer  together,  and  as 
the  cords  are  attached  to  the  same  point  in  front,  if  the 
back  ends  are  brought  closer  together,  the  front  part 
of  the  cords  will  touch  each  other,  and  thus  virtually 
shorten  the  cord. 


82  PHYSIOLOGY. 

110.  The  Larynx  as  a  wind  instrument. — But  the 

larynx  is  not  merely  a  stringed  instrument;  perhaps 
it  has  more  points  in  common  with  wind  instruments. 
In  these  the  notes  are  varied  by  the  size  of  the  aperture 
through  which  the  air  is  forced  into  the  tube,  by  the 
length  of  the  tube,  and  by  the  velocity  with  which  the 
air  enters  it.  Now,  as  the  thyroid  cartilage  is  drawn 
upward,  and  the  vocal  cords  are  made  tense  and  brought 
nearer  to  each  other  by  the  movement  of  the  arytenoid 
cartilages,  the  glottis  is  diminished  in  size,  while  the 
tube  (which  consists  of  the  mouth  and  nasal  passages) 
is  shortened  by  the  amount  that  the  thyroid  cartilage 
is  elevated. 

But  when  the  organs  of  voice  are  placed  in  this  con- 
dition, more  force  is  required  to  expel  the  usual  quan- 
tity of  air  from  the  lungs,  and  thus  the  last  condition 
of  a  high  pitch  is  secured.  This  explains  why  it  is 
more  fatiguing  to  speak  or  sing  on  a  high  key  than  on 
a  lower  one. 

111.   Modulation  of  Articulate   Sounds.— But   the 

utterance  of  musical  sounds,  and  the  performance  of 
most  wonderful  musical  combinations,  are  not  the  most 
important  or  most  difficult  functions  of  the  vocal  ap- 
paratus. The  rapid  adjustment  of  the  larynx,  by  the 
movements  of  a  very  complicated  system  of  muscles, 
in  the  articulations  of  a  rapid  speaker,  is  one  of  the 
most  marvelous  of  all  the  phenomena  of  the  animal 
economy. 

While  all  vocal  sounds  are  formed  in  the  larynx,  yet 
voice  thus  formed  is  modulated  in  the  mouth  and  nasal 
passages.  The  organs  concerned  in  modulation  of  voice 
are  chiefly  the  lips,  teeth,  tongue,  palate,  and  air  pass- 


NERVOUS  SYSTEM.  83 

ages  of  the  nose.  All  have  observed  how  the  voice  is 
affected  by  the  loss  of  the  front  teeth,  or  by  the  imper- 
fect palate  and  lip  in  persons  with  harelip.  The 
tongue,  though  important,  is  not  the  sole  organ  in 
modulating  articulate  sounds. 

Recapitulation. 

The  larynx  is  the  organ  of  voice.  It  is  composed  of  five 
cartilages.  Voice  is  produced  by  the  vibration  of  the  vocal 
cords.  These  are  put  in  motion  by  air  forced  through  the 
glottis  from  the  trachea. 

The  larynx  has  the  properties  of  both  a  stringed  and  a  wind 
instrument  Various  means  of  modifying  pitch,  etc.  Rapid 
movement  of  the  vocal  organs  in  speaking.  Modulation  of 
sound  in  the  mouth  and  nasal  passages. 


LESSON    XIV. 

NERVOUS  SYSTEM. 

112.  Distribution  of  Yital  Force,  a  brain  func- 
tion.—  The  organs  which  we  have  described,  with 
their  functions,  are  simply  the  machinery  of  life.  We 
have  not  yet  looked  into  the  engine-room  from  which 
the  power  is  furnished  to  operate  this  wonderful  ma- 
chinery, enabling  it  to  perform  the  various  functions 
of  the  living  body.  The  instrument  through  which 
this  power  is  distributed  to  every  organ  of  the  body,  is 
the  nervous  system. 

This  consists  of  the  Spinal  cord,  Brain,  and  the 
nerves  by  which  every  organ  is  connected  with  these 
great  centers  of  vital  force.  It  has  been  customary  to 


84 


PHYSIOLOGY. 


consider  the  brain  as  the  primary  organ,  and  the  spinal 
cord  and  nerves  as  appendages  to  it;   but  we  find,  in 

FIG.  49.— FRONT  AND  BACK  VIEW  OF  THE  BRAIN 
AND  SPINAL  CORD. 


«,  a.  Cerebellum.     6,  6.  Cerebrum,     c,  c.  Spinal  cord. 
d.  Medulla  oblongata. 

the  lowest  class  of  vertebrate  animals  (the  fishes),  that 
the  brain  is  very  imperfectly  developed,  while  the 
spinal  cord,  with  its  nerves  distributed  to  all  parts 
of  the  animal,  is  very  perfectly  formed. 

113.  Cereforo-spinal  and  Oanglionic  Systems.  —  In- 
deed, we  find  in  living  bodies  this  ascending  scale : 
in  vegetables  we  have  no  trace  of  anything  like  a 
nervous  system ;  in  the  invertebrate  forms  of  life,  we 
find  nerves  distributed  to  the  adjacent  organs  from  local 
nervous  centers,  called  ganglions,  but  no  brain  or  spinal 
cord;  in  fishes,  the  brain  is  little  more  than  an  enlarge- 


NERVOUS   SYSTEM. 


85 


FIG.  50.— BRAIN— FRONT 
VIKW. 


ment  of  the  forward  end  of  the  cord.  As  we  ascend  the 
scale  of  vertebrate  life,  however,  we  find  the  brain  be- 
coming more  and  more  promi- 
nent, till  we  reach  the  summit 
of  perfection  in  man. 

The  spinal  cord  and  brain  are 
generally  regarded  by  anatomists 
as  a  single  organ,  which  they 
call  the  Cerebro-spinal  axis. 
The  existence  of  this  cerebro- 
spinal  axis,  in  vertebrate  ani- 
mals, does  not  supersede  or  dis-  a-  Right  ht-mi*Phere  of  lhe 
place  the  system  of  ganglions, 
as  found  in  the  lower  types  of 
animal  life.  This  constitutes 
what  is  known  as  the  Sympa- 
thetic system. 


cerebrum.     6.  Left  hemi- 
sphere of  the  cerebrum. 

FIG.  51.— BRAIN— SIDE 
VIEW. 


114.  The  Two  Hemispheres.  c " 

—  The  cerebro- spinal  nervous 
system  is  symmetrical,  being 
divided  into  right  and  left  sides, 

a.  Anterior  lobe  of  the  cere- 

corresponding   exactly  in  num-       brum.  6.  inferior  lobe.  c. 

her,     Size,     and    position     of    the          Posterior  lobe.  d.  Cerebel- 

parts.  In  accordance  with  this 
arrangement,  the  brain  is  sep- 
arated, by  a  deep,  vertical  fissure, 
into  the  right  and  left  hemi- 
spheres. This  separation  is  not 
quite  perfect,  for,  near  the  base 
of  the  brain,  a  broad  band  of 
fibers  extends  from  one  hemisphere  to  the  other,  thus 
forming  a  connection  between  them. 


lam. 


FIG.  52.— CEREBELLUM— 

RACK  VIEW. 


86 


PHYSIOLOGY. 


BASE  OF  THE  BRAIN. 


Transversely,  the  brain  is  divided  into  the  Cerebrum 
or  large  brain,  occupying  the  upper  and  front  part 
of  the  skull,  and  the  Cerebellum  or  small  brain,  sit- 
uated at  the  posterior  base  of  the  cranium.  The  spinal 
cord  is  divided  longitudinally  by  a  deep  fissure,  both 
on  the  front  and  back,  leaving  only  a  narrow  bridge 
of  the  substance  of  the  cord  in  its  center. 

115.  Medulla  Oblongata— membranes  of  the  brain.— 

The  spinal  cord  enters  the  cranium  at  the  large  open- 
ing in  its  base,  called 
the  Foramen  Magnum, 
and  extending  upward 
and  forward,  forms  a 
connection  with  the 
cerebellum  backward, 
and  with  the  cerebrum 
above.  This  portion 
of  the  spinal  cord  ly- 
ing within  the  skull 
is  called  the  Medulla 
Oblongata.  It  is  a 
kind  of  bulb,  or  en- 
largement of  the  up- 
per end  of  the  cord, 
and  consists  of  three  pairs  of  bodies  (Pyramidal,  Resti- 
form,  and  Olivary),  which  are  united  pretty  firmly 
together. 

Both  the  brain  and  spinal  cord  are  securely  wrapped 
in  membranes.  The  outer  one  of  these,  the  Dura  Mater, 
is  a  dense,  firm  membrane,  adhering  strongly  to  the 
inner  surface  of  the  skull.  The  Pia  Mater  is  a  very 
delicate  membrane,  attached  to  the  surface  of  the  brain ; 


a 


a.  Medulla  oblongata.     ft.  Pons  varolii. 
c.  Olfactory  nerves,     d.  Optic  nerves. 


NERVOUS    SYSTEM.  87 

and  as  this  surface  is  uneven,  or  convoluted,  the  Pia 
Mater  dips  down  between  these  convolutions,  separating 
them  from  each  other.  Between  these  membranes  lies 
a  fine,  gauze-like  coat,  called  the  Arachnoid  membrane. 
These  serous  membranes  are  subject  to  diseases  both 
dangerous  and  difficult  to  cure. 

116.  Gray  and  White  Matter  of  the  Brain.— The 

substance  of  which  the  brain  is  composed  is  very  soft,  and 
easily  broken  down  in  handling  it.  Being  composed 
largely  of  albumen,  it  may  be  rendered  quite  firm  by 
steeping  it  for  some  days  in  alcohol,  after  which  it  may 
be  studied  very  satisfactorily.  Like  all  other  life-formed 
tissues,  its  ultimate  form  is  the  cell,  or  little  globe. 
These  cells,  however,  change  their  shape  more  rapidly 
in  the  brain  than  in  any  other  tissue  of  the  body. 

The  brain  is  not  uniform  throughout  in  its  texture 
and  appearance.  In  both  the  cerebrum  and  cerebellum, 
the  central  portion  of  the  organ  is  nearly  a  clear  white, 
and  appears  under  the  microscope  to  be  fibrous  in  its 
texture.  Surrounding  this,  and  following  the  irregular- 
ities of  the  convolutions,  we  find  a  layer  of  gray  or 
ash-colored  matter,  differing  in  thickness  in  different 
persons,  but  forming  a  marked  feature  of  every  brain. 
In  the  spinal  cord,  the  relative  position  of  these  parts 
is  inverted,  the  gray  matter  being  in  the  center,  and 
the  white  surrounding  it. 

117.  Gray  and  White  Matter.— The  proportion  of 
gray  matter  to  the  white  is  greater  in  the  cerebrum 
than  in  the  cerebellum  or  spinal  cord;  and  the  nervous 
cords  distributed  from  these  to  all  parts  of  the  body  are 
made  entirely  of  white  matter,  though  the  gray  sub- 
stance appears  again  in  the  center  of  the  ganglions,  or 

B.  P.— 8. 


88 


PHYSIOLOGY. 


FIG.  54.— TRANSVERSE  SECTION  OF 
THE  CERKKRUM. 


little  brains  attached  to  the  sympathetic  system.     The 

gray  matter  consists  of 
cells,  often  very  irregular 
in  their  shape,  and  con- 
stantly changing  form. 
The  white  part,  while  it 
appears  to  be  made  of 
fibers,  is  really  composed 
of  chains  of  cells,  forming 
continuous  tubuli,  extend- 
ing from  the  gray  part  of 
the  brain  to  the  extremi- 
ties of  the  nerves. 


118.  Cranial  Nerves. — 

The  nerves  are  cords  com- 
posed of  a  white  substance 
like  that  of  the  brain,  extending  to  all  the  living  tissues 


a,  a.  Gray  matter  of  the  brain.   6,  6. 
White  matter,  c.  Corpus  callosum. 


FIG.  55.— ORIGIN  OF  THK  CRANTAT,  NERVES. 


a.  Cerebrum.  6.  Cerebellum,  c.  Arbor  vltse.  d.  Corpus  callosum.  e. 
Medulla  oblongata.  /.  Olfactory  nerve,  g.  Optic  nerve,  h.  Trifacial 
nerve,  f.  Auditory  nerve. 

erf  the  body,  and  connecting  all  the  organs  with  the  gray 


NERVOUS   SYSTEM. 


matter  of  the  brain  or  spinal  cord.  These  nerves  are 
arranged  in  pairs,  corresponding  to  each  other  on  the 
different  sides  of  the  body.  Twelve  pairs  of  these  come 
off  within  the  skull,  and  are  sent  to  the  different  organs 
on  which  they  are  distributed  through  openings  in  the 
bones.  These  are  called  Cranial  nerves. 

The  first  and  second  pairs,  being  the  Olfactory  and 
Optic  nerves,  appear  to  come  off  from  the  lower  part 
of  the  front  lobe  of  the  cerebrum,  but  their  principal 
fibers  have  been  traced  backward  to  the  upper  part 
of  the  medulla  oblongata.  The  fifth  pair,  immediately 
after  passing  out  of  the 
skull,  divides  into  three 
branches.  From  this  fact 
it  is  sometimes  described 
as  three  nerves.  The 
ninth  and  tenth  pairs, 
as  they  leave  the  skull 
through  the  same  open- 
ing, have  been  described 
as  one  pair  by  some  anat- 
omists. 

119.  Spinal  Nerves.— 

The    spinal    cord    gives 

origin  to  thirty-one  pairs 

of  nerves,  eight  of  which 

come  off  from  the  spinal 

cord  in  the  neck,  and  are 

called    Cervical    nerves ; 

twelve  in  the  back,  which 

are  named  Dorsal  nerves;  five  from  the  loins,  which  are 

known   as    Lumbar  nerves;   and  six   pairs  come   from 


FIG.  56.  — Ouiorx  OF  THE  SPINAL, 
X i  i:vrs. 


a 


a,  a.  Bracliial  plexns. 
plexus. 


6,  6.  Lumbar 


90  PHYSIOLOGY. 

the  termination  of  the  cord  in  the  sacrum,  and  are  called 
Sacral  nerves.  The  four  lower  cervical  and  the  upper 
dorsal  nerves  on  each  side  unite  with  each  other,  and 
separate  again  to  be  distributed  on  the  upper  extremity. 
This  is  called  the  Brachial  Plexus.  The  last  dorsal 
*nd  the  five  lumbar  nerves  form  a  similar  combina- 
don,  called  the  Lumbar  Plexus. 

Recapitulation. 

The  nervous  system  is  the  distributer  of  vital  force.  It  con- 
sists of  spinal  cord,  brain,  and  nerves.  The  nervous  system  is 
symmetrical,  being  divided  into  right  and  left  sides. 

The  two  hemispheres  are  connected  by  the  corpus  callosum. 
The  brain  consists  of  cerebrum,  cerebellum,  and  medulla  ob- 
longata. 

The  brain  consists  of  an  outer  gray  substance  made  of  cells, 
and  an  inner  white  matter  composed  of  fibers,  or  tubuli. 

The  nerves  connect  all  the  organs  with  the  brain  and  spinal 
cord. 


LESSON   XV. 

NERVOUS    SYSTEM. —  CONTINUED. 

120.  Complex  Function  of  the  Brain.  —  The  organs 
comprising  the  systems  of  nutrition  and  voluntary 
motion  have,  as  a  general  rule,  but  a  single  function 
each;  but  in  the  nervous  system  this  rule  is  violated. 
The  spinal  cord  and  brain,  considered  as  a  single  organ, 
performs  at  least  three  distinct  and  independent  func- 
tions :  1st.  it  is  the  source,  either  directly  or  indirectly, 
of  all  muscular  motion ;  2d.  it  is  the  seat  of  sensation ; 
and,  3d.  it  is  the  organ  of  thought. 


NERVOUS    SYSTEM.  91 

These  several  functions,  if  not  absolutely  independent 
of  each  other,  are  so  in  a  degree  that  is  truly  wonderful. 
The  intellectual  powers  may  be  deranged  so  as  to  pro- 
duce a  true  insanity,  with  scarcely  any  disturbance 
of  the  functions  of  motion  or  sensation.  On  the  other 
hand,  in  paralysis  there  may  be  entire  loss  of  motion  or 
sensation  in  many  of  the  organs,  while  the  mental 
activity  remains  unimpaired. 

121.  Nerves   of  Special   Sense.  —  The  functions  of 
motion  and  sensation  are  carried  on  by  the  brain  exclu- 
sively through  the  agency  of  nerves,  but  the  connection 
of  the  brain  with  the  intellectual  phenomena  appears  to 
have  no  direct  association  with  them. 

The  first,  second,  and  eighth  pairs  of  nerves  are  de- 
voted exclusively  to  special  sensations.  The  first  pair 
are  appropriated  to  the  sense  of  smell,  and  are  therefore 
called  the  Olfactory  nerves.  They  are  distributed  on 
the  mucous  membrane  of  the  nasal  cavities.  The  sec- 
ond pair  are  the  Optic  nerves,  which  furnish  the  eye 
with  the  power  of  vision.  The  nerves  of  hearing  are 
the  eighth  pair.  They  are  distributed  on  the  internal 
ear,  and  are  the  only  cranial  nerves  that  do  not  pass 
out  of  the  skull.  The  sense  of  taste  is  the  function  of  a 
branch  of  the  fifth  and  eighth  pair  of  nerves  on  each  side. 

122.  Motor    and    Sentient    Nerves.  —  The    nervous 
trunks  which  perform  the  mixed  functions  of  sensation 
and  motion  originate  by  two  separate   roots,  each  de- 
voted to  its  appropriate  office.     This  is  more  distinctly 
seen  in  the  spinal  nerves,  where,  at  each  joint  of  the 
spinal  column,  nerves  pass  out,  right  and  left,  from  the 
spinal  cord.     These  have  each  an  anterior  and  a  pos- 
terior root,  the  first  originating  from  the  front,  and  the 


92 


PHYSIOLOGY. 


FIG.  57.— MOTOR  AND  HEX- 

TIKNT  ROOTS  OF  TIIK 

SIMXAT.  NE::VK. 

a.  ,b 


last  from  the  back  part  of  the  spinal  cord.  If  the  an- 
terior root  be  injured  or  diseased,  the  power  of  motion 
is  lost  or  impaired  in  the  parts 
to  which  the  nerve  is  distributed; 
but  if  the  injury  is  in  the  poste- 
rior root,  the  power  of  sensation, 
or  feeling,  is  impaired  in  the 
parts  supplied  by  that  nerve. 
The  anterior  is  therefore  called 
the  Motor  root,  and  the  posterior 
the  Sentient. 

123.  Distribution  of  Nerves. 

— The   sentient    root   is   slightly 

larger  than   the   motor,  and  has 
posterior  root  with   its    a  ganglion  or  enlargement  on  it 

just   before   it    joins    its   fellow. 

This  union  takes  place  before 
the  nerve  passes  through  the  opening  between  the 
vertebra?,  and  beyond  this  the  nervous  cord  appears 
to'  consist  of  but  one  kind  of  fibers  or  tubuli,  but  at  the 
termination  of  the  nervous  branches  the  distinction  of 
function  is  again  observed. 

The  nervous  trunks,  by  sending  off  branches,  dis- 
tribute 'themselves  over  the  parts  they  are  intended  to 
supply.  In  this  distribution,  though  the  branches  of 
nerves  are  sent  to  almost  every  organ  of  the  body,  yet 
the  supply  furnished  to  different  organs  is  not  by  any 
means  the  same. 

124.  Motor  and  Sentient  Nerves  terminate  differ- 
ently.—  The  nerves  of  motion  and  those  of  sensation 
differ  most  widely  in  their  functions,  yet  the  most 
careful  examination  with  the  best  microscope  fails  to 


«,   a.    Anterior,,  or    motor 
root.      6,    6.  Sentient  or 


ganglion,  exposed  by  re- 
moving the  motor  root. 


NERVOUS    SYSTEM.  93 

reveal  any  difference  in  their  structure  so  long  as  the 
fibers  remain  wrapped  in  the  same  nervous  envelope; 
but  as  we  trace  the  nervous  trunks  toward  their  ex- 
tremities, the  filaments  of  different  functions  separate 
from  each  other,  and  in  their  terminations  there  is  a 
very  marked  difference  in  their  appearance.  The  nerves 
of  motion  continue  to  divide,  until  their  filaments  be- 
come so  fine  that  even  the  microscope  scarcely  enables 
us  to  trace  them.  They  are  distributed  entirely  to  the 
muscular  system,  and  terminate  on  the  ultimate  cells 
composing  the  muscular  fibers,  and  communicate  to 
them  the  power  by  which  the  fiber  is  shortened,  and, 
consequently,  the  whole  muscle  contracted. 

125.  Facinian  Corpuscles. — The  nerves  of  sensation, 
as  they  approach  their  extremities,  are  usually  folded 
back  on  themselves,  so  as  to  form  a  kind  of  loop;  and 
sometimes  this  folding  is  repeated  two  or  three  times, 
so  as  to  produce  a  distinct  enlargement  at  the  end  of 
the    nervous    filament.      This   repeated   folding   of   the 
nervous  tubuli  forms  what  are  called  Pacinian  corpus- 
cles.    They  are  found  in  the  nerves  terminating  on  the 
hand  and  foot  more  frequently  than  in  any  other  part 
of  the  body.     They  appear  to  be  connected  with  the 
special  sense  of  touch,  as  they  are  found  in  the  upper 
lip  of  the  horse,  and  in  the  end  of  the  elephant's  trunk. 
Some  have  supposed  them  to  be  organs  for  producing 
animal    electricity,    as    they    resemble    somewhat    the 
organs  of  certain  electric   fishes. 

126.  Sentient  Nerves  on  the  Skin.  —  But  the  single 
loop,  or  simple  folding  back  on  themselves,  is  a  mode 
of  termination  common  to  all  sentient  nerves,  whether 
the  sensation  is  merely  feeling,  or  is  some  special  form 


94  PHYSIOLOGY. 

of  sensation,  as  seeing,  hearing,  tasting,  or  smelling. 
The  surface  of  the  skin  is  so  well  furnished  with 
sentient  nerves,  that  it  is  impossible  to  put  down  the 
point  of  a  needle  anywhere  on  it  without  touching  one 
of  those  loops  terminating  a  nervous  filament,  and 
thus  communicating  to  the  brain  intelligence  of  the 

FIG.  58.— NERVES  OF  SENSATION,  WITH  THEIH  TERMINAL,  LOOPS 

GUEATLY    MAGNIFIED. 


injury.  By  this  arrangement,  every  part  of  the  body 
that  is  liable  to  be  injured  by  foreign  substances,  is 
kept  in  constant  communication  with  the  brain,  where 
consciousness  resides,  and  from  whence  proceed  all 
voluntary  motions. 

127.  Mystery  of  Sensation.  —  This  power  of  feeling 
is  a  wonderful  endowment.  An  impression  is  made  on 
a  looped  extremity  of  a  sentient  nerve,  in  some  remote 
part  of  the  body.  Instantly,  the  filament  of  nerve 
thus  impressed  communicates  the  impression  along 
the  nervous  cord,  where  this  particular  filament  is 
entangled  and  interlaced  with  a  thousand  similar  ones ; 
and  yet  the  impression  is  not  communicated  to  them, 
but  is  confined  to  the  individual  filament;  it  passes 
through  the  interior  white  matter  of  the  brain,  and 
finally  reaches  the  gray  substance,  where  perception 
or  consciousness  appears  to  reside.  This  perception 
not  only  locates  the  precise  spot  where  the  impression 


NERVOUS    SYSTEM.  95 

was  made,  but  also  determines  the  nature  of  the  im- 
pression, and,  within  certain  limits,  the  character  of 
the  substance  or  agent  making  it. 

128.  Injury  of  a  Nervous  Trunk. — The  office  of  the 
nerves  is  illustrated  in  the  phenomenon  of  a  paralyzed 
limb.  If  the  great  nervous  trunks,  returning  to  the 
brain  the  impressions  made  on  any  particular  part 
of  the  body,  be  destroyed,  the  person  has  no  knowledge 
of  the  condition  of  that  part;  but  if  the  injury  be 
partial  or  temporary,  the  perception  will  be  impaired 
or  confused  as  to  the  place  of  the  impression  or  its 
nature.  Thus,  by  an  improper  attitude,  we  sometimes 
compress  the  nervous  trunk  conveying  impressions 
from  the  hand  or  foot,  and  a  peculiar,  prickling  sen- 
sation is  felt  in  the  part  on  which  the  nerve  ter- 
minates. This  is  expressed  in  common  language  by 
saying  that  the  hand  or  foot  "  is  asleep." 

Recapitulation. 

The  nervous  system  performs  the  functions  of  motion,  sensa- 
tion, and  thought.  Nerves  devoted  to  sensation  alone,  have  but 
a  single  origin ;  nerves  of  both  sensation  and  motion,  originate 
by  two  roots.  Nerves  of  sensation  terminate  in  loops;  those  of 
motion  by  filaments  distributed  on  the  muscles.  Between  their 
origin  and  termination  the  nervous  trunks  are  alike.  When 
impressions  are  made  on  the  trunk  of  a  sentient  nerve,  the 
sensation  is  referred  to  the  extremity. 
B.  P.— 9. 


96  PHYSIOLOGY. 


LESSON  XVI. 

SENSATION. 

129.  Low  Sensibility  of  Bone,  Cartilage,  etc.— The 
power  of  sensation  is  not  distributed  alike  to  all   the 
organs  of  the   body.     The  bones  and  cartilages  have  no 
feeling  when  in  a  healthy  condition;   but  when  they 
are    inflamed,   they  become    highly  sensitive.     This   is 
probably    owing    to    some    peculiar    condition    of    the 
nerves    in   the   solid  substance .  of  these  tissues,  which 
is  not  well  understood, 

The  fatty  deposits,  which  often  accumulate  to  a  con- 
siderable thickness  between  the  skin  and  muscles,  as 
well  as  in  other  parts  of  the  body,  are  nearly  destitute 
of  feeling,  having  but  few  nerves  distributed  on  them. 
The  muscles  which  produce  the  voluntary  motions  of 
the  body,  while  they  are  the  only  points  of  distribution 
for  the  motor  nerves,  are  but  moderately  supplied  with 
nerves  of  sensation ;  and  consequently  the  muscles,  when 
in  a  healthy  condition,  have  but  little  feeling.  The 
organs  of  involuntary  motion,  such  as  the  heart,  etc., 
are  entirely  insensible,  except  in  a  diseased  state. 

130.  Sense  of  Touch  in  the  Fingers.  — The  skin, 
and    the    mucous    membrane    lining    the    mouth    and 
glottis,  are  the  chief  seats  of  sensation.     The  skin,  on 
different    parts  of   the  body,   has   different    degrees   of 
sensibility.    The  fingers  and  toes  have  the  largest  num- 
ber of  sentient  nerves  distributed  on  their  surfaces,  and, 
consequently,  have   the   most  acute  sensibility  of  any 
of  the  organs  of  the  body.     Indeed,  the  surface  of  the 


SENSATION.  97 

true  skin  on  the  ends  of  the  fingers  appears  to  be  made 
up  of  bundles  of  sentient  nerves,  or  their  loop-like 
terminations,  forming  those  little  elevations,  called  the 
papillae,  which  cover  these  parts.  So  highly  endowed 
with  sensibility  are  these  organs,  that  some  have  re- 
garded them  as  special  instruments  of  a  local  sense, 
differing  from  the  general  sensibility  of  the  body;  but 
the  function  appears  to  differ  in  degree,  rather  than  in 
kind. 

131.  The  Grades  of  Sensation— Muscular  Sense,— 

A  careful  analysis  of  this  subject  will  reveal  at  least 
three  distinct  "grades  of  sensibility,  located  in  different 
organs  of  the  body ;  and,  in  some  of  them,  the  sensation 
varies  in  acuteness  in  different  parts  of  the  organ  or 
organs  to  which  the  sensation  is  referred.  First  in  the 
group  of  sensations,  and  lowest  in  the  distinctness  of  its 
impressions  on  the  perceptive  powers,  is  the  subjective 
or  internal  sense,  sometimes  called  the  muscular  sense. 
The  most  obscure  manifestation  of  this  is  in  those  sen- 
sations which  we  call  weariness,  fatigue,  faintness,  etc. 
These  sensations  appear  to  be  rather  general  than 
special,  and  therefore  can  hardly  be  referred  to  any 
particular  locality  in  the  body. 

The  sensation  of  weight,  or  resistance  to  muscular 
action,  is  a  little  better  defined,  but  still  very  difficult 
to  locate.  If  we  extend  the  hand,  and  place  a  piece 
of  card-paper  on  the  fingers,  we  will  perceive  merely 
the  sensation  of  touch;  but  if  a  two-pound  weight  be 
substituted  for  the  card,  a  very  different  sensation  is 
felt  —  a  perception  of  what  we  call  weight. 

132.  Sense    of  Touch,   of  Taste    and    Smell.  — A 

second  class  comprises  those  sensations  which  are  made 


98  PHYSIOLOGY. 

by  contact  with  external  objects,  and  referred  definitely 
to  the  point  of  contact,  and  also  where  the  perception 
determines  something  in  relation  to  the  character  of  the 
body  producing  the  sensation. 

For  example,  the  sense  of  touch  determines  where 
the  person  is  touched,  and  whether  the  substance  pro- 
ducing the  sensation  -  is  rough  or  smooth,  hard  or  soft, 
hot  or  cold,  etc.  But  the  tongue  not  only  conveys  to 
the  brain  the  sensation  of  being  touched,  and  the  usual 
knowledge,  of  the  physical  properties  of  the  body  touch- 
ing it,  but  also  a  peculiar  sensation  which  is  called 
taste.  It  is  -  a .  special  sensation,  and  is  definitely  re- 
ferred to  the  mouth.  So,  also,  the.  olfactory  nerves  convey 
to  the  brain  the  sensation  produced  by  odorous  bodies. 

133.  Organs  of  the  Sense  of  Smelling.  — This  second 
group  of  sensorial  functions  ascends,  in  point  of  delicacy, 
from  the  mere  sense  of  contact  common  to  the  whole 
surface  of  the  body,  to  the  sense  of  smell,  which  recog- 
nizes odors  so  exceedingly  delicate  that  no  other  test 
can  detect  their  presence.  This  sense  has  a  pair  of 
nerves  especially  appropriated  to  it;  and  though  the 
sentient  extremities  of  these  nerves  are  distributed  on 
the  mucous  membrane  of  the  nasal  passages,  which 
differs  nothing  in  appearance  from  the  mucous  mem- 
brane forming  the  surface  of  other  open  cavities,  yet 
the  delicacy  of  the  olfactory  sense  falls  but  little  below 
that  of  senses  of  the  third  class,  each  of  which  has 
a  special  apparatus  appropriated  to  its  use.  In  some 
of  the  lower  animals,  such  as  the  dog  and  the  vulture, 
this  sense  is  much  more  acute  than  in  man.  Many 
animals  which  live  in-  the  water  have  the  sense  of 
smell  greatly  developed. 


SENSATION.  99 

134.  Use    of  the   Turbinated    Bones.  — The   nasal 
cavities   have   their  surfaces  greatly  extended  by  the 
turbinated  bones.     These  are  thin  plates  of  bone,  rolled 
up  and  placed  one  in  each  nasal  chamber,  and  covered 
throughout  with  the  membrane,  on  which  the  olfactory 
nerves  are  distributed. 

.These  air  passages  are  so  placed  that  the  air,  in 
ordinary  breathing,  scarcely  enters  them ;  but  when  a 
voluntary  effort  is  made  to  exercise  the  function  of 
smelling,  it  is  drawn  forcibly  through  the  passages,  and 
made  to  enter  the  cavities  among  the  folds  of  the 
turbinated  bones,  and  thus  greatly  to  increase  the 
surface  in  contact  with  the  odors  inhaled.  There 
appears  to  be  a  strange  complication  of  the  sense  of 
smell  with  that  of  taste,  so  that  much  of  what  is  usually 
regarded  as  taste  really  belongs  to  the  olfactory  sense. 

135.  Simple  Nature  of  the  Olfactory  Sense.— The 

sense  of  smell  appears  to  be  the  least  complicated  of  all 
our  sensations.  When  we  place  our  hand  on  the  table, 
we  liave,  first,  a  sense  of  contact  with  something  exter- 
nal to  ourselves;  then,  in  quick  succession,  the  sensa- 
tions which  determine  hardness,  smoothness,  tempera- 
ture, etc.,  each  one  of  which  appears  to  be  the  exercise 
of  a  special  function,  but  all  taken  together  form  the 
complex  sensation  which  we  call  feeling.  On  the  other 
hand,  if  we  inhale  a  powerful  odor,  such  as  musk,  for 
example,  we  have  no  distinct  sensation  of  contact,  no 
clear  perception  of  any  thing  outside  of  ourselves,  no 
indication  of  the  direction  from  which  the  odor  came, 
no  ideas  of  size  or  shape  are  derived  from  the  sensation ; 
all  we  acquire  is  a  knowledge  of  that  indefined  property 
called  odor. 


100  PHYSIOLOGY. 

A  singular  fact  about  the  exercise  of  this  sense  is 
that,  while  we  distinguish  odors,  and  identify  them  as 
the  property  of  certain  substances,  yet  we  have  no 
names  for  odors,  but  describe  them  only  by  com- 
parison. 

136.  Ability  to  suffer  Pain,  important  to  our 
Safety,  —  These  lower  grades  of  sensation  are  of  the 
utmost  importance  to  the  safety  and  enjoyment  of  the 
individual.  The  senses  of  taste  and  smell  are  the  chief 
guides  on  which  we  rely  in  the  selection  of  our  food; 
and  the  sense  of  feeling,  which  rises  to  pain  when  the 
contact  is  violent,  continually  admonishes  us  of  danger 
from  surrounding  objects.  Our  safety  depends  more  on 
our  ability  to  suffer  pain  than  most  persons  apprehend. 
Those  who,  from  disease  or  accident,  have  lost  the  sense 
of  feeling  in  a  limb,  often  sustain  serious  injury,  from 
burns  or  other  accidents,  before  they  are  aware  of 
danger.  These  senses  may  therefore  be  regarded  as 
body-guards  or  sentinels,  placed  on  the  outposts  of  the 
citadel  of  life  to  give  timely  warning  of  the  approach 
of  friend  or  foe. 

Recapitulation. 

Sensation  is  unequally  distributed  among  the  organs.  Sense 
of  feeling  is  distributed  over  the  surface  of  the  body  generally. 
Special  sense  of  touch  located  in  the  ends  of  the  fingers. 
Three  grades  of  sensations:  1st,  muscular  sense;  2d,  touch, 
taste,  and  smelling;  3d,  seeing  and  hearing.  Olfactory  sense 
located  in  the  nasal  passages.  Peculiar  arrangement  of  the 
turbinated  bones.  Smelling  the  least  complicated  of  all  the 
menses. 


THE  EAR.  101  , 


LESSON    XVII. 

ORGANS   OF   SPECIAL   SENSE. 

137.  Senses  which  have  Special  Organs.— The  third 
and  highest  class   of  sentient  functions  have  each  a 
special  apparatus  appropriated  to  them,  by  means  of 
which  they  make  us  acquainted  with  properties  and 
conditions  of  bodies  around   us,  that   are   entirely  be- 
yond   the    reach    of   ordinary    sensation.     The    special 
senses  of  hearing  and  seeing  form  this  class. 

The  Ear,  the  organ  of  hearing,  consists  of  the  external 
ear,  the  tympanum  or  middle  ear,  and  the  labyrinth  or 
internal  ear.  The  external  ear  consists  of  a  tube  about 
an  inch  in  length,  which  in  man  and  in  most  mam- 
mals spreads  out  into  a  broad  expansion  externally. 
Both  the  tube  and  the  expanded  rim  are  formed  of  a 
firm,  elastic  cartilage.  In  birds  and  reptiles  the  exter- 
nal expansion  is  wanting;  and,  in  fishes,  the  rudiments 
of  the  internal  ear  are  found,  but  no  vestige  of  an  outer 
ear  has  been  discovered. 

138.  The   External   Ear.  —  In  the  human  subject, 
the  external  expansion  forms  an  irregular,  semicircular 
plate,  concave  on  its  forward  and  outer  surface,  and  cor- 
respondingly convex  on  the  opposite  side.     Its  purpose 
is  to  collect  and  concentrate  the  vibrations  of  the  air  at 
a  central  point,  which  is  the  external  opening  of  tho 
auditory  tube. 

This  opening  is  protected  from  the  intrusion  of  dust, 
insects,  etc.,  by  a  cluster  of  stiff,  short  hairs  placed  near 
the  -  entrance ;  but  a  more  effectual  protection  is  afforded 


102 


PHYSIOLOGY. 


by  a  yellow,  tenacious,  bitter  wax,  secreted  by  a  number 
of  small  glands  on  the  inner  surface  of  the  auditory 
tube.  Across  the  bottom  of  this  tube  is  drawn  a  fine 
membrane,  so  as  to  close  it  completely,  and  thus  cut 
off  all  communication  with  the  middle  ear. 


FIG.  59— THE  EAK. 


fl 


\ 


139.  Drum  of  the  Ear— Eustachian  Tube.  — The 

Tympanum,  or  drum  of  the  ear,  is  a  cavity  in  the 
hard  portion  of  the  temporal  bone.  While  it  is  cut 
off  from  direct  communication  with  the  external  air 
by  the  drum-head,  or  membrane  of  the  tympanum,  just 
now  described,  that  communication  is  indirectly  estab- 
lished through  the 
posterior  chamber  of 
the  mouth,  by  means 
of  a  funnel-shaped 
^nal,  called  the  Eu- 
stachian  tube.  The 
narrow  end  of  this 
tube  passes  through 
a  small  opening,  or 
foramen,  into  the 
cavity  of  the  middle 
ear,  while  the  broad 
end  establishes  a 
communication  with 
the  upper  portion  of 
the  pharynx,  and  by 
this  means  the  tympanum  is  kept  filled  with  air.  In 
yawning,  the  Eustachian  tube  is  compressed,  and  some- 
times the  sides  temporarily  adhere  together,  occasioning 
an  unpleasant  roaring  in  the  head,  till,  with  a  crackling 
sound,  the  obstruction  is  removed,  and  all  is  right  again. 


n.  External  ear.  6.  Auditory  tube.  c.  Tym- 
panum, or  middle  ear.  d.  Semicircular 
canals,  e.  Vestibule.  /.  Cochlea,  g.  Eu- 
stachian tube. 


THE  EAR. 


103 


FIG.  60.— BONES  OF  THE  MIDDLE 
EAR,  ENLARGED. 


C- 


a.  Malleus,  or  the  hammer,  b.  In- 
cus, or  the  anvil,  c.  Orbiculare,  or 
the  round-bone,  d.  Stapes,  or  the 
stiri'up. 


140.  Bones  of  the  Ear.  —  In  the  cavity  of  the  tym- 
panum there  are  four  small  bones,  articulated  together 
so    as    to    form    a    bony 

chain,  stretching  from  the 

tympanic    membrane    to 

the  membrane  closing  the 

aperature  communicating 

with  the  inner  ear.  These 

bones    are    named,    from 

their  fancied  resemblance 

to  the  objects,  the  malleus, 

or  hammer;  the  incus,  or 

anvil;    the   orbiculare,    or 

round-bone ;  and  the  stapes, 

or  stirrup.     The  handle  of  the  hammer  is  fastened  to 

the  middle  of  the   drum-head,  while   the  head  of  the 

hammer  fits  into  the  cavity  of  the  anvil,  and  the  horn 

of  the  anvil  is  attached,  by  means  of  the  round-bone,  to 

the  bow  of  the  stirrup,  the  base  of  which  rests  firmly 

against   the   membrane   closing   the   passage   into   the 

labyrinth. 

141.  Injuries  of  the  Middle  Ear  — their  effect.  - 

This  chain  of  bones  is  furnished  with  very  delicate 
muscles,  which  serve  to  render  it  tense,  so  that  the 
slightest  vibration  is  transmitted  along  it  from  the 
outer  to  the  inner  ear.  These  bones  are  sometimes 
destroyed  by  disease  or  accident,  without  the  entire 
loss  of  hearing,  though  always  with  great  injury  to 
that  function. 

The  dullness  of  hearing  common  to  old  age  is  usually 
the  result  of  the  growing  together  of  this  bony  chain, 
as  well  as  of  the  thickening  of  the  membranes  at  each 


104 


PHYSIOLOGY. 


end  of  the  chain.  These  changes  are  often  accompanied 
by  the  more  or  less  complete  closure  of  the  Eustachian 
tubes.  While  perfect  deafness  seldom  results  from  inju- 
ries to  the  middle  ear,  yet  most  of  the  causes  which 
operate  to  merely  impair  hearing  are  located  there. 

142.  The  Labyrinth,  or  Internal  Ear.  — The  Laby- 
rinth   is   composed  of  three  parts:    the   vestibule,  the 
semicircular  canals,  and  the  cochlea,  or  snail-shell.    The 
vestibule    is   a   common   chamber  with   which  all   the 
other  parts  communicate.     It  is  a  small,  oblong,  irregu- 
larly shaped  cavity  in   the    hard   portion   of  the   tem- 
poral bone,  with  two  small  openings  looking  into  the 
middle  ear.     These  are  called  finestrse,  or  windows,  and 
from  their  respective  shapes  are  named  the  oval  and 
the   round   windows.     These,   in   the   living   body,  are 
closed  by  a  dense,  firm  membrane,  but,  in  the  skeleton, 
appear  as  openings  from  one  chamber  to  the  other. 

143.  The  Semicircular  Canals — their  use. — Some 

idea  of  the  form  and 
relation  of  the  several 
parts  of  the  inner  ear 
may  be  obtained  from 
the  annexed  figure, 
which  represents  the 
internal  ear,  somewhat 
enlarged. 

The  semicircular  ca- 
nals, three  in  number, 
are  simply  curved 
openings  through  the 
bony  substance  sur- 
rounding this  cavity,  passing  out  of  the  vestibule  and 


FIG.  61.— THK  INTEKNAL  EAK. 


a.  Vestibule.  6.  Cochlea,  c.  Semicircu- 
lar canals,  d.  The  oval  window,  e. 
The  round  window. 


THE  EAR.  105 

returning  to  it.  If  they  serve  any  other  purpose  than 
to  extend  the  surface  for  the  distribution  of  the  auditory 
nerve,  that  purpose  has  not  been  discovered. 

144.  The  Cochlea.  —  The  Cochlea,  or  snail-shell,  is  a 
double  spiral  canal,  wound  around  a  central  pillar. 
Leaving  the  vestibule  opposite  to  the  oval  window,  it 
makes  two  and  a  half  turns  around  the  pillar  and 
reaches  the  summit,  where  it  enters  the  other  canal, 
and  by  the  same  number  of  turns  as  in  ascending,  it 
descends  to  the  vestibule,  reaching  it  at  the  round 
window.  All  these  cavities  are  filled  with  a  limpid 
fluid,  which  is  nearly  pure  water;  and  they  are  lined 
by  a  very  delicate  membranous  expansion  of  the  audi- 
tory nerve.  In  the  vestibule  and  semicircular  canals, 
this  nervous  expansion  is  covered  with  filaments,  or 
loops  of  nerve  matter,  floating  loosely  at  one  extremity, 
and  attached  to  the  nervous  mass  by  the  other.  In  the 
cochlea,  the  nervous  expansion  presents  a  smooth,  soft 
surface. 

Recapitulation. 

Seeing  and  hearing  are  senses  with  special  organs  devoted  to 
them.  The  ear  consists  of  the  external,  middle,  and  internal 
divisions.  The  middle  ear  communicates  with  the  mouth  by 
the  Eustachian  tube.  It  contains  a  chain  of  four  small  bones. 
Its  cavity  is  filled  with  air.  The  internal  ear  consists  of  a 
vestibule,  a  cochlea,  and  three  semicircular  canals.  These 
cavities  are  filled  with  water.  The  auditory  nerve  is  distributed 
on  the  membrane. 


106  PHYSIOLOGY. 


LESSON    XVIII. 

HEARING. 

145.  Nature  of  Sound.  —  The  complex  organ  which 
we  attempted  to  describe  in  the  last  lesson,  is  intended 
to  convey  to   the  brain  the  sensation  of  sound,  and  its 
several  properties  and  qualities.     The  sense  of  hearing 
takes   cognizance   of  a   tremulous   or  vibratory  motion 
transmitted  through  a  medium  (usually  the  air)  from  a 
vibrating   body,   to   the  -auditory   nerve    in   the    inner 
ear. 

All  bodies  are  not  capable  of  emitting  sound.  Elas- 
ticity and  hardness  are  the  properties  which  are  com- 
monly assigned  to  sonorous  bodies,  but  this  definition 
appears  to  be  defective.  Two  currents  of  air  striking 
each  other  will  give  out  sound,  without  the  assistance 
of  any  hard  substance.  Elasticity  is  an  indispens- 
able property  of  sonorous  bodies,  and  yet  but  few  sub- 
stances are  more  elastic  than  India  rubber,  and  none 
less  sonorous. 

146.  Transmission  of  Sound-waves. — A  bell  is  struck 
with  a  hammer,  and  instantly  the  particles  of  which  it 
is  composed  are  thrown  into  a  kind  of  wave-like  motion, 
which  is  prolonged  for  several  seconds.     This  vibration 
can  be   easily  perceived  if   we  bring  our  fingers   into 
contact  with    the    bell    immediately  after    the    stroke. 
This  movement  is  transmitted  to  the  surrounding  air, 
and   waves   of    motion,   exactly   corresponding    to    the 
vibrations  in  the  bell,   roll  off  in  every  direction,  di- 
minishing, however,  in  intensity  as  they  recede  from 


HEAHING.  107 

the  sonorous  body,  but  retaining  all  the  other  properties 
of  the  original  vibration  in  the  bell. 

Air  is  not  the.  only  medium  of  communication 
between  sounding  bodies  and  the  organ  of  hearing. 
Dense  solids,  such  as  the  metals,  compact  wood,  etc., 
are  good  conductors  of  sound,  and  water  transmits 
sonorous  vibrations  very,  perfectly. 

147.  Conditions  of  the  Transmission  of  Sound.— 

Sound  is  not  transmitted  through  a  vacuum,  hence  a 
bell  struck  in  the  exhausted  receiver  of  an  air-pump 
gives  out  no  sound,  because  there  is  nothing  in  contact 
with  it  to  communicate  its  vibrations  to  the  outer  air. 
Sound  is  transferred  with  difficulty  from  one  medium 
to  another.  A  bell  struck  under  water  gives  scarcely 
any  sound  to  the  ear  in  the  air,  but  if  the  ear  be  under 
water,  the  sound  is  almost  deafening. 

Though  wood  is  an  excellent  conductor  of  sound,  yet 
a  wooden  partition  of  but  an  inch  in  thickness  greatly 
interrupts  th.e  passage  of  sounds.  This  is  because  the 
vibrations  have  to  be  transferred  to  the  wood  from  the 
air,  and  after  .passing,  the  wood,  re-transferred  to  the  air 
again,  by  which  a  large  proportion  of  the  original  in- 
tensity is  lost.  Air  contained  in  a  tube  transmits  sound 
much  more, perfectly  than  when  unconfined,  because  the 
vibrations  are  not  readily  communicated  to  the  sur- 
rounding walls  of  the  tube. 

148.  Reflected  Sound.  —  Waves  of  sound,  transmitted 
through  the  air,  striking  on  a  solid  surface,  communi- 
cate but   a  small  amount  of  their  motion    to   the  ob- 
structing   solid.     The    greater    portion    is    reflected   or 
turned  back  again  into  the  same  medium.     This  re- 
flected wave  of  sound  forms  what  is  called  the  echo, 


108  PHYSIOLOGY. 

and  is  always  less  intense  than  the  original  sound,  by 
the  amount  of  vibration  communicated  to  the  reflecting 
surface.  Obeying  the  law  of  reflection,  sound  may  be 
concentrated  by  being  reflected  from  concave  surfaces, 
and  diffused  when  thrown  off  from  convex  ones.  On 
tkis  principle  ear-trumpets  act,  to  collect  at  a  single 
point  the  sonorous  vibrations  of  a  large  space.  The 
cartilaginous  expansion  of  the  outer  ear  serves  the 
same  purpose. 

149.  Mechanism  of  Hearing.  —  The  undulations,  or 
waves  of  sound,   thus   concentrated  by  the   expansion 
of  the  external  ear,  strike  on  the  tense  membrane  of 
the    tympanum   at   the    bottom   of  the    auditory  tube, 
communicating   to  it  similar  vibrations.     But   as   one 
end  of  the  chain  of  bones  in  the  middle  ear  is  attached 
to  the  tympanic  membrane,  whatever  state  of  motion  is 
induced  in  it  will  be  transmitted  along  the  bony  con- 
nections to  the  stirrup,  the  base  of  which  presses  firmly 
against  the  membrane  of  the  oval  window. 

The  arrangement  of  these  bones  is  such  as  to  slightly 
magnify  the  movement,  and  to  limit  it  to  a  single 
direction.  The  stirrup-bone  moves  to  and  from  the 
membrane  with  which  it  is  in  contact,  and  can  have 
no  lateral  or  side  motion.  But  the  inner  ear,  in  all  its 
parts,  being  filled  with  fluid,  has  the  vibration  of  the 
membrane  communicated  to  it  throughout,  by  the  well- 
known  law  of  the  transmission  of  impressions  through 
fluids. 

150.  The   Qualities   of  Sound.  —  The   expansion   of 
the  auditory  nerve  being  every-where  in  contact  with 
this  fluid,  and  its  sentient  loops  floating  loosely  in  it, 
transmits  to  the  brain  the  intelligence  of  the  vibration. 


HEARING.  109 

The  sensation  thus  conveyed  to  the  seat  of  perception 
is  an  exceedingly  complex  one,  embracing,  beside  the 
simple  impression  of  sound,  the  almost  innumerable 
qualities  and  modifications  of  it. 

The*  chief  of  these  may  be  comprised  in  the  intensity 
or  force,  the  pitch,  and  the  direction  of  sound.  The 
force  or  loudness  of  a  sound  is  often  mistaken  for  its 
pitch,  because  a  sound  on  a  high  key  produces  the 
jarring  sensation  of  a  much  louder  sound  on  a  lower 
key.  The  length  of  the  undulations,  or  what  is  the 
same  thing,  the  number  of  vibrations  in  a  given  time, 
constitutes  the  pitch  of  a  sound,  without  any  reference 
to  the  force  by  which  the  vibration  is  set  in  motion. 

151.  The  Direction  of  Sound,  how  determined. — 

The  power  to  determine  the  direction  from  which  a 
vibration  proceeds,  is  not  the  least  of  the  wonders  of 
this  wonderful  sense.  If  we  were  to  reason  from  the 
mechanical  arrangement  of  the  ear,  we  would  infer  that 
all  sounds,  when  communicated  to  the  auditory  nerve 
through  the  tube  of  the  external  ear,  the  chain  of  bones 
in  the  middle  ear,  and  the  fluid  of  the  labyrinth,  would 
be  converted  into  waves  in  a  uniform  direction;  but 
this  is  not  the  case.  As  the  wave  of  sound  rolls 
out  in  every  direction  from  the  vibrating  body,  it  is 
evident  that  a  line  drawn  from  that  body  must  cut  the 
wave  at  right-angles,  at  whatever  point  it  may  strike  it. 
That  which  the  auditory  sense  determines,  therefore,  is 
the  direction  of  a  line  that  shall  be  at  right-angles  with 
the  undulations.  In  a  practiced  ear,  this  delicate  task 
is  performed  with  amazing  accuracy. 

152.  Musical   Faculties.  —  But  the  nice  discrimina- 
tions of  a  well  disciplined  musical  ear,  are  even  more 


110  PHYSIOLOGY. 

wonderful  than  the  measurement  of  the  angle  necessary 
to  determine  the  direction  of  sound.  This  is  a  special 
faculty,  and  does  not  depend  alone  on  the  acuteness  of 
hearing.  Many  persons  who  hear  accurately  even  very 
feeble  sounds,  and  judge  correctly  of  their  other  prop- 
erties, yet  distinguish  the  pitch  of  sounds  very  im- 
perfectly. Many  eminent  physiologists  have  referred 
this  faculty  to  the  cochlea  or  spiral  canals,  and  there 
appears  to  be  plausible  reasons  for  such  reference. 
However,  in  the  present  state  of  anatomical  knowledge, 
it  would  be  hazardous  to  affirm  any  thing  on  the  subject. 
The  power  to  distinguish  the  voice  of  a  particular 
person,  is  really  as  strange  as  the  most  wonderful 
musical  powers. 

153.  The  Sense  of  Hearing  —  how  far  it  is  vol- 
untary.—  The  sense  of  hearing  is  properly  an  invol- 
untary function,  though  there  are  several  modifications, 
subject  to  the  will,  which  have  an  important  bearing 
on  the  exercise  of  this  faculty.  For  example,  if  the 
attention  be  directed  to  a  certain  sound,  we  can,  by  a 
voluntary  effort,  transmit  that  sound  to  the  perceptive 
center,  and  practically  exclude  all  others,  though  they 
may  be  more  forcible. 

There  is  also  a  voluntary  power  of  increasing  the 
tension  of  the  tympanic  membrane,  thus  rendering  the 
ear  more  sensitive,  and  capable  of  hearing  very  feeble 
sounds.  The  sense  of  hearing  can  be  educated,  in  its 
several  departments,  to  an  almost  unlimited  extent, 
as  is  witnessed  in  the  trained  musician,  and  the 
telegraph  operator. 

The  organs  essential  to  hearing  being  located  in  a 
bony  cavity,  are  subject  to  fewer  accidents  than  most 


THE  EYE.  Ill 

of  the  other  organs;  but  a  long  continued  exposure  to 
loud  and  constant  noises,  as  in  machine-shops  and 
factories,  greatly  impairs  the  acuteness  of  hearing. 

Recapitulation. 

The  ear  acquaints  us  with  sound  and  its  qualities.  Hard, 
elastic  bodies,  when  vibrating,  communicate  their  motion  to  the 
air,  or  other  medium  with  which  they  are  in  contact.  This 
vibration  is  transmitted  to  the  inner  ear  through  the  drum  by 
means  of  the  bony  chain,  and  a  similar  motion  is  set  up  in  the 
fluid  of  the  internal  ear.  The  auditory  nerve  transmits  to  the 
brain  the  knowledge  of  this  vibration.  The  brain  recognizes 
the  sound — its  force,  pitch,  direction,  etc.  Hearrng  is  involun- 
tary, but  may  be  modified  by  volition. 


LESSON    XIX. 

THE    EYE. 

154.  Muscles  of  the  Eye.  — The  Eye,  the  organ  of 
vision,  consists  of  the  globe  or  ball  of  the  eye,  the 
adjusting  machinery,  and  the  protecting  organs.  The 
two  last-named  divisions,  however,  are  merely  auxiliary 
organs,  and  not  absolutely  essential  to  vision.  The 
adjusting  machinery  consists  of  six  muscles,  which 
arise  from  the  back  part  of  the  bony  socket  in  which 
the  ball  of  the  eye  is  placed.  Four  of  these  are  called 
straight  muscles.  They  are  inserted  into  the  back  part 
of  the  orbit,  about  equal  distances  apart,  so  that  while 
two  serve  to  roll  the  eye  upward  and  downward,  the 
other  two  give  it  a  lateral  motion  to  the  right  and 

left. 

B.  P.— 10. 


112  PHYSIOLOGY. 

The  remaining  two  are  called  oblique  muscles.  They 
are  inserted  into  the  outside  of  the  eyeball,  and  operate 
to  roll  it  inward  and  downward.  One  of  these  has  a 
peculiar  contrivance  for  this  purpose.  It  arises  with 
the  straight  muscles  from  the  back  of  the  orbit,  but  is 

FIG.  62.— MUSCLES  OF  THE  EYE. 

e 


a 


a.  Globe  of  the  eye.  6,  6,  6.  Straight  muscles,  c.  Muscle  to  raise 
the  upper  eyelid  (Levator  Palpebrce).  d.  Upper  oblique  muscle. 
e.  Loop  and  tendon.  ' 

carried  forward  and  upward  by  a  slender  tendon,  which 
passes  through  a  loop  of  firm  ligament  attached  to  the 
upper  and  inner  margin  of  the  bony  socket  of  the  eye, 
from  whence,  turning  back,  it  is  inserted  into  the  outer 
and  back  part  of  the  ball. 

155.  Arrangements  for  Protecting  the  Eye. — The 

protecting  organs  are  several,  and,  taken  together,  con- 
stitute a  very  perfect  system  of  protection  to  a  very 
delicate  organ,  whose  function  requires  that  it  shall 
have  a  large  external  exposure.  The  ball  of  the  eye, 
the  true  organ  of  vision,  is  placed  in  a  deep,  bony 
socket,  the  margin  of  which  is  guarded  above  by  a 
heavy  ridge  of  bone  in  the  form  of  an  arch.  The  eye- 
ball, in  this  cavity,  rests  on  a  soft,  elastic  cushion  of 


THE   EYE. 


113 


fatty  matter,  which  entirely  fills  the  back  part  of  the 
socket. 

The  eyelids  are  a  pair  of  curtains,  with  each  a  thick, 
cartilaginous  edge  fitting  accurately  to  its  mate,  and 
thus  completely  excluding  the  eye  from  the  outer  world. 
These  margins  are  lined  with  short,  curved  hairs,  the 
eyelashes,  which  serve  as  a  screen  to  protect  the  eye 
from  dust.  The  bony  ridge  above  the  eye  is  also  cov- 
ered with  a  line  of  short,  thick  hairs,  inclining  toward 
the  outer  angle  of  the  eye,  so  as  to  carry  the  perspira- 
tion around  that  organ. 

15(5.  Tears — their  use  —  the   Lachrymal  Duct. — 

That   it   may  perform  its  function  correctly,  the   eye 

FIG.  63.— LACHRYMAL  GLAND  AND  DUCT. 


a.  Lachrymal  gland.  6.  Ducts  leading  from  the  gland  to  the 
upper  part  of  the  eye.  c,  c.  The  lachrymal  points,  d.  Nasal 
duct. 

requires  to  be  kept  constantly  moist.  To  accomplish 
this  end,  a  gland,  called  the  Lachrymal  gland,  is  placed 
in  a  depression  of  the  orbit  immediately  back  of  the 
arch,  at  its  upper  and  outer  part.  This  gland  secretes 
the  fluid  called  tears,  and,  from  its  situation,  this  secre- 


114 


PHYSIOLOGY. 


tion  is  very  readily  distributed  over  the  front  part  of 
the  ball,  by  the  motion  of  the  eyelids  in  winking. 

The  inner  surface  of  the  eyelid  is  covered  with  a 
very  delicate  and  highly  sensitive  membrane,  called 
the  conjunctiva.  This  is  reflected  off  from  the  eyelid 
to  the  ball,  and  covers  the  front  part  of  it,  one  layer 
of  it  passing  entirely  over  the  transparent  cornea  in 
front  of  the  eye.  The  tears,  after  having  performed 
their  office,  are  conveyed  into  the  nose  by  the  lach- 
rymal duct,  which  opens  into  the  orbital  cavity  near 
the  inner  angle  of  the  eye. 

157.  Coats  of  the  Eye.  — The  ball  of  the  eye  is  a 

complete  optical  instrument,  a  camera  of  the  same 
kind  used  by  artists  in  making  sun-pictures,  but  in- 
finitely more  perfect 
than  any  instrument 
which  human  ingen- 
uity and  skill  has  yet 
produced.  The  eye  has 
three  distinct  coats. 
The  outer  one  of  these, 
called  the  Sclerotic 
coat,  is  a  dense,  tough 
membrane,  approach- 
ing nearly  to  the  firm- 

a.  The  three  coats  of  the  eye.    6.  The      n6SS  of  Cartilage, 
cornea,     c.  The   aqueous   humor,     d.  Qn      the      front      part 

of  the  ball,  this  coat 
changes  its  character, 
becomes  transparent  and  slightly  thinner,  but  preserves 
its  hardness.  This  transparent  portion  is  called  the 
Cornea.  It  is  more  convex  than  the  sclerotic  coat 


FIG.  64.— THE  EYE. 


The  crystalline  lens.     e.  The  vitreous 
humor.    /.  Optic  nerve. 


THE  EYE.  115 

elsewhere,  as  if  it  were  a  segment  cut  from  a  smaller 
sphere.  The  Choroid  coat  is  a  highly  vascular  mem- 
brane, lying  in  immediate  contact  with  the  inner  sur- 
face of  the  sclerotic  coat.  It  contains  numerous  cells 
filled  with  a  dark  brown  or  black  pigment,  which  gives 
its  color  to  the  membrane. 

158.  Iris,    Pupil,    and    Ciliary    Processes.  —  That 
portion   of   the   choroid   coat   which   lies   back    of  the 
cornea,   is  separated  from  it  by  a  considerable   space, 
and  in  this  part  it  takes  the  name  of  Iris.     The  iris 
is  a  colored  curtain,   with   a  circular  opening   in  the 
center  called  the  Pupil. 

On  the  back  of  the  iris,  and      FIG.  65.-inis,  PUPIL,  AND 

CILIARY  PROCESSES. 

attached  to  the  outer  margin 
of  it,  is  a  series  of  firm,  liga- 
mentous  bodies,  arranged  like 
rays  around  the  iris.  These  are 
the  Ciliary  processes.  To  the 
inner  end  of  these  is  attached  a 
number  of  very  fine,  muscular 
fibers,  with  their  opposite  ends 

,   .     .  ,,  , ,          «.  Pupil,     b.  Iris.     c.  Ciliary 

inserted  into  the  margin  of  the  processes. 

pupil.      When    these    contract, 

they   draw    the   curtain   back,    and    thus    enlarge    the 

pupil. 

There  is  also  a  set  of  circular  fibers,  the  contraction 
of  which  serves  to  draw  the  curtain  forward,  and  thus 
diminish  the  pupil.  These  motions  are  produced,  in- 
voluntarily, by  the  effect  of  light. 

159.  The  Retina.  — The  Retina  forms  the  third  coat 
of  the  eye,  and  lies  directly  in  contact  with  the  vitreous 
humor  which  fills  the  greater  portion  of  the  ball.     This 


116  PHYSIOLOGY. 

is  a  very  delicate  membrane,  made  up  of  a  net-work  of 
nervous  filaments  interwoven  with  minute  blood-vessels, 
so  as  to  form  a  continuous  membrane.  These  filaments 
are  expansions  of  the  optic  nerve,  which,  though  it  is 
the  largest  nervous  trunk  in  the  body,  is  confined  in  its 
expansion  exclusively  to  the  inner  coat  of  the  eye.  It 
is  limited  in  its  function  to  the  special  sense  of  sight, 
and  though  so  sensitive  to  the  effect  of  light,  it  is  in- 
capable of  feeling  the  grosser  impressions,  when  in  a 
normal  or  healthy  condition;  but  when  inflamed,  it 
becomes  very  sensitive. 

160.  Aqueous    Humor  —  its   position.  —  The    space 
between  the  cornea  and  iris  is  filled  with  a  transparent 
fluid,   which    is   nearly   pure    water.     It    is   called   the 
Aqueous  humor.     Its  shape  is  that  of  a  plano-convex 
lens,  and  it  affects  the  rays  of  light  that  enter  it  in 
precisely  the   same   manner  that   such  a  lens  does  in 
optical    instruments. 

In  surgical  operations  on  the  eye,  the  aqueous  humor 
is  sometimes  discharged;  but  if  the  opening  be  closed, 
and  the  light  carefully  excluded  from  the  eye,  the  water 
will  be  reproduced  in  a  few  days.  This  fluid  fills  not 
only  the  space  between  the  cornea  and  the  iris,  but 
also  that  back  of  the  iris,  to  the  suspensory  ligament 
of  the  crystalline  lens. 

161.  Crystalline  Lens. — The  Crystalline  Lens  is  the 
principal  organ  in  the  apparatus  of  vision.     It  is  situ- 
ated immediately  behind  the  pupil,  and  is  held  in  place 
by  a  thin  suspensory  ligament,  attached  to  the  outer 
margin  of  the  ciliary  processes.     It  is  a  soft  solid,  very 
transparent,  and,  in  shape,  a  double  convex  lens,  with 
the  posterior  surface  more  convex  than  the  front.     It  is 


VISION.  117 

capable  of  being  separated  into  concentric  layers,  some- 
what like   the  coats  of  an  onion,  the     „ 

f  JGr«    Do*  —  L,O?f CEJf » 

layers  becoming  constantly  denser  as      TRIC  LAYERS  OF 
we   penetrate   toward   its  center.  THE  CRYSTALLINE 

T  F*XS 

The  muscular  bands  attached  to  the 
ciliary  processes  have  the  power  of 
adjusting  the  crystalline  lens,  so  as  to 
accommodate  the  vision  to  objects  at 
different  distances  from  the  eye.  Back 
of  the  crystalline  lens,  the  ball  of  the 
eye  is  filled  with  a  transparent  semi- 
fluid, somewhat  resembling  the  white 
of  an  egg.  It  is  the  vitreous  humor,  and  is  in  contact 
with  the  retina  at  all  points. 

Recapitulation. 

Provisions  for  protecting  the  eye.  Eyebrows,  their  use.  Tears 
secreted  by  the  lachrymal  gland,  and  distributed  over  the  eye- 
ball in  winking.  Conjunctiva  covers  the  inner  surface  of  the 
eyelid.  The  eyeball  has  three  coats  —  the  sclerotic  coat,  the 
choroid,  and  the  retina.  The  front  projection  of  the  sclerotic 
coat  is  transparent— it  is  the  cornea.  The  front  part  of  the 
choroid  coat  is  the  iris;  the  opening  through  it,  the  pupil. 
The  retina,  the  inner  coat,  is  a  nervous  membrane.  The  aqueous 
humor  lies  between  the  cornea  and  iris.  The  crystalline  lens 
lies  behind  the  pupil. 


LESSON   XX. 

VISION. 

162.  Mechanism  of  Tision.  — The  Eye  is  an  optical 
instrument  which,  by  the  most  perfect  adaptation  of  its 
parts,  produces  an  image  of  external  objects,  and  casts 


118  PHYSIOLOGY. 

it  on  a  sensitive  screen  in  the  back  part  of  a  dark- 
ened chamber.  It  is,  therefore,  a  true  camera  obscura 
with  two  lenses,  and  a  very  transparent  medium  be- 
tween the  last  lens  and  the  retina,  where  the  image 
appears. 

In  order  to  understand  how  the  mechanism  of  the  eye 
operates  to  produce  vision,  it  will  be  necessary  to  state 
a  fundamental  law  governing  the  movement  of  light  in 
passing  through  mediums  of  different  density. 

163.  Refraction  of  Light.  — Rays  of  light  are  thrown 
off  from  luminous  bodies  in  every  direction,  and  move 
in    straight    lines    so    long   as   they   continue    to   pass 
through  the  same   medium.     When  light   passes  from 
one  medium  into  another,  as  from  air  into  water,  the 
ray  is  bent  out  of  its  course,  unless  it  enters  on  a  line 
perpendicular  to  the  surface. 

This  bending  of  a  ray  out  of  a  straight  line  is  called 
the  refraction  of  light.  Different  substances  have  different 
refractive  powers.  A  ray  of  light  passing  from  the  air 
into  water,  on  a  line  oblique  to  its  surface,'  is  bent 
downward,  or  refracted  toward  a  line  perpendicular  to 
the  surface  of  the  water;  and  a  r-ay  passing  from  water 
into  the  air,  is  refracted  in  the  opposite  direction  —  that 
is,  from  the  perpendicular. 

164.  Reflection   of  Light  from  Opaque  Bodies.— 

A  lens  is  a  transparent  medium  bounded  by  curved 
lines.  These  may  make  the  surfaces  either  concave  or 
convex,  and  the  effect  of  the  lens  on  rays  of  light  will 
correspond  to  the  shape.  A  convex  lens  converges  or 
brings  the  rays  together,  while  the  effect  of  a  concave 
lens  is  to  cause  the  rays  to  diverge  from  each  other. 
Rays  of  light  are  thrown  off,  not  only  from  luminous 


VISION. 


119 


bodies,  but  from  all  substances  which  afford  any  obstruc- 
tion to  light  in  passing  through  them.  The  latter  re- 
flect the  rays  of  light,  which  thus  appear  to  come  from 
the  reflecting  surface  as  though  it  originated  there.  Most 
bodies  are  visible,  therefore,  only  by  reflected  light. 

FIG.  67.— A  DOUBLE  CONVEX  LENS,  SHOWING  THK  REFRACTION 
OF  LIGHT. 


a,  a.  A  double  convex  lens.      b.  Parallel  rays  of  light,      c.  The 
focus,  or  point  where  the  converging  rays  meet. 

165.  Aqueous  Humor  and  Crystalline  Lens.  —  The 

transparent  cornea,  forming   the  front  of  the  eye,  re- 


FIG.  68.— FORMATION  OF  IMAGES  IN  THE  EYE. 


a.  The  cornea,  b.  The  aqueous  humor,  c,  c.  The  iris,  d,  d.  The 
sclerotic  coat.  e.  The  crystalline  lens.  /.  The  optic  nerve. 
g.  The  vitreous  humor,  h.  The  pupil. 

ceives  the   rays  of  light  on  a  convex  surface;   and  it, 

with    the    aqueous    humor    lyin^    back    of    it,    being 
B.  P.— 11. 


120  PHYSIOLOGY. 

denser  than  the  air,  causes  the  rays  to  converge. 
Now  rays  coming  to  the  eye  from  objects  near  it, 
do  not  reach  the  cornea  parallel  with  each  other, 
but  are  diverging.  This  first  lens  (the  aqueous  hu- 
mor), therefore,  serves  chiefly  to  correct  this  diverg- 
ence, and  bring  the  light  to  the  crystalline  lens  in 
parallel  rays.  This  lens  is  denser  than  the  aqueous 
humor,  and  consequently  refracts  the  light  conveyed  to 
it.  Both  its  surfaces  are  convex,  with  the  back  more  so 
than  the  front;  therefore  the  rays,  in  passing  into  the 
vitreous  humor,  are  so  converged  that  they  form  a  focus 
on  the  retina,  in  the  posterior  chamber  of  the  eye. 

166.  Place  and  Size  of  the  Image.  — Rays  of  light 
thrown   off  divergent  from   every   point  of  an  object, 
would  therefore   be   converged  to  a  focus,  and  form  an 
image;    and   when   the    eye    is    properly  adjusted,  this 
image    will    be    in   direct   contact    with   the    sensitive 
surface  of  the  retina.     This  surface  transmits  the  im- 
pression thus  made  to  the  brain,  where  the  perceptions 
of  it  are  recorded. 

By  a  law  in  optics,  the  image  becomes  smaller  as  the 
distance  of  the  object  from  the  lens  is  increased.  In 
looking  at  a  distant  landscape,  the  whole  scene,  with 
its  mountains,  rivers,  and  forests,  covering  many  square 
miles,  is  faithfully  delineated  on  a  surface  scarcely 
more  than  a  quarter  of  an  inch  square;  and  yet  so 
perfect  is  the  image  of  each  object,  that  the  mind 
clearly  perceives  it. 

167.  Images  on  the  Retina  are  Inverted.  —  But  the 

rays  of  light  coming  from  the  lower  part  of  an  object, 
will  form  their  focus  at  the  upper  part  of  the  image; 
and  those  from  the  upper  part  of  the  object,  crossing 


VISION.  121 

the  first,  will  form  the  lower  part   of  the   image,  so 
that  the  picture  will  be  inverted. 

This  is  well  known  to  be  the  position  of  the  image 
formed  in  a  camera  obscura,  an  instrument  constructed 
on  the  principle  of  the  eye ;  and  it  has  been  further 
proven  by  actual  experiment.  If  we  take  the  eye  of 
an  ox,  and  carefully  dissect  the  sclerotic  and  choroid 
coats  away  from  the  back  part  of  it,  and  fit  the 
eye  thus  prepared  into  an  opening  in  a  shutter,  so 
that  the  cornea  will  look  outward,  and  then  place 
ourselves  behind  the  eye,  in  a  dark  room,  we  shall 
see  the  images  of  external  objects  in  an  inverted 
position  on  its  retina. 

168.  How  Olyects  are  seen  Erect.  —  Many  physi- 
ologists  have   been   greatly    puzzled    to    explain    why 
objects  appear  erect,   when  the   images  by   which   we 
see  them  are  inverted;  but  if  we  remember  that  vision 
is  an  acquired  function,  and  that  we  learn  the  position, 
size,  and  form  of  things  seen,  only  by  habit,  the  diffi- 
culty disappears  at  once. 

Universal  experience  teaches  us  that  the  part  of  the 
image  impressed  on  the  lower  portion  of  the  retina, 
answers  to  the  upper  part  of  the  object ;  and,  reversely, 
impressions  on  the  higher  parts  of  the  eye  answer  to 
the  lower  portion  of  objects.  Indeed,  none  of  the 
special  senses  give  us  knowledge  instinctively,  but  all 
require  to  be  trained  and  educated,  till  the  perceptive 
powers  become  familiar  with  their  modes  of  commu- 
nicating intelligence. 

169.  Adjustment   of  the   Eye.  —  But    there    is    an- 
other difficulty  connected  with  the  mechanism  of  the 
eye,  more  serious  than  this.     Rays  coming  from  distant 


122  PHYSIOLOGY. 

objects  are  nearer  parallel  than  those  radiating  from  a 
less  remote  point,  and  rays  entering  the  eye  least  di- 
vergent will  come  to  a  focus  soonest;  consequently,  if 
the  distance  between  the  crystalline  lens  and  the  retina 
were  always  the  same,  and  the  shape  of  the  lens  un- 
alterable, we  would  be  able  to  see  objects  distinctly 
only  in  one  place. 

If  they  were  nearer  to  us,  the  image  would  fall 
behind  the  retina;  if  farther  from  us,  it  would  be 
formed  in  the  vitreous  humor  in  front  of  that  surface. 
This  difficulty  is  remedied  by  accommodating  the  posi- 
tion or  shape  of  the  crystalline  lens  to  the  distance  of 
the  object  from  the  eye.  The  muscular  fibers  of  the 
ciliary  processes  (§  161),  draw  the  lens  forward  when 
we  look  at  things  near  us,  which  movement  also  com- 
presses the  lens,  so  that  its  focus  is  shortened;  and 
these  joint  movements  throw  the  image  on  the  sensitive 
surface  of  the  retina. 

Recapitulation. 

Images  are  formed  in  the  eye  by  the  refraction  of  light. 
Self-luminous  bodies,  and  those  reflecting  light,  are  objects  of 
vision.  The  aqueous  humor  corrects  the  divergence  of  light; 
the  crystalline  lens  is  chiefly  concerned  in  forming  the  image. 
The  distance  of  the  object  diminishes  the  size  of  the  image. 
Perfect  vision  requires  that  the  image  be  in  contact  with  the 
retina.  Images  in  the  eye  are  inverted.  Position,  size,  and 
place  of  an  object  are  determined  by  habit.  The  eye  adjusts 
itself  to  the  varying  location  of  objects. 


VISION.  123 


LESSON    XXI. 

VISION.  —  CONTINUED. 

170.  Spherical  Aberration — its  cause  and  effect.— 

The  quantity  of  light  admitted  into  the  eye  is  meas- 
ured by  its  intensity.  In  a  strong  light,  fewer  rays  are 
required  to  form  a  distinct  image;  and  accommodating 
itself  to  this  condition,  the  pupil  is  diminished  by  the 
circular  fibers  of  the  iris  contracting,  and  drawing  the 
edge  of  the  curtain  forward.  In  a  dim  light,  this  move- 
ment is  reversed,  and  the  radiating  fibers  of  the  iris 
draw  the  edge  back,  and  thus  enlarge  the  pupil.  But 
in  using  the  eye  with  an  enlarged  pupil  in  a  dim  light, 
objects  become  indistinct,  with  their  outlines  no  longer 
sharply  defined. 

This  results  from  a  well-known  principle  in  optics. 
The  rays  of  light  which  Ml  near  the  edge  of  a  convex 
lens  are  bent  more,  and  consequently  have  a  shorter 
focal  distance  than  those  falling  near  the  axis  of  the 
lens,  thus  making  the  focus  a  line,  rather  than  a  point. 
This  is  called  spherical  aberration.  The  contraction  of  the 
iris  covers  the  edges  of  the  crystalline  lens,  and  thus 
avoiding  spherical  aberration,  leaves  the  image  sharply 
defined  when  made  by  a  bright  light. 

171.  Short-sightedness.  —  Short-sightedness    is    gen- 
erally attributed  to  a  too  great  convexity  of  the  cornea. 
In  a  majority  of  cases  of  this  kind,  the  defect  in  vision 
arises  from  this  cause,  but  it  evidently  may  be  produced 
by  a  too  great  convexity  of  the  crystalline  lens,  as  well 
as  by  the  same  deformity  of  the  cornea;  or  there  may  be 


124 


PHYSIOLOGY. 


FIG.  60.— SHORT-SIGHTEDNESS. 


The  image  formed  forward  of  the 
retina. 


too  great  a  distance  between  the  lens  and  the  retina. 

This  may  be  owing  to  a  defect  in  the  power  of  adjust- 
ment in  the  eye.  If  the 
cause  of  near-sighted- 
ness lies  in  the  cornea, 
age  will  cure  it ;  if  it  is 
from  either  of  the  other 
causes,  it  will  remain. 
Long-sightedness  arises 
from  the  opposite  condi- 
tions. This  is  seen  in 
FIG.  70.-LoNG-siGHTEDNEss.  faQ  subjoined  figures. 

I  .** — 
\s 

172.  Size  and  Dis- 
tance of  Objects — how 
determined. — The  abil- 

The  image  formed  back  of  the  retina.      ity      to      determine      the 

distance  and  size  of  ob- 
jects seen  is  acquired  only  by  practice.  The  size  of  an 
object  would  very  naturally  be  inferred  from  the  space 
occupied  by  the  image  on  the  retina ;  but  a  small  object 
near  the  eye  will  make  an  image  covering  as  much  of 
the  retina  as  a  large  one  at  a  distance.  From  this  it 
will  be  seen  that  size  and  distance  are  intimately  re- 
lated in  vision. 

If  we  know  the  distance  of  an  object,  we  may  form 
a  pretty  accurate  judgment  of  its  size;  and,  on  the 
other  hand,  having  determined  the  size  of  any  thing, 
we  readily  refer  it  to  the  proper  distance.  Painters 
avail  themselves  of  this  law  by  introducing  into  pic- 
tures of  buildings,  landscapes,  etc.,  figures  of  men  or 
animals  whose  size  is  well  known,  and  by  this  means 
they  enable  us  to  judge  correctly  of  the  distance  of  the 


VISION.  125 

objects,  which  the  perspective  may,  perhaps,  have  failed 
to  determine  positively. 

173.  Transparency  of  the  Atmosphere  affects  the 
Judgment  of  Distance.  —  The  degree  of  distinctness 
in  the  outlines  and  general  form  of  bodies,  furnishes 
another  means  of  determining  distance.     This  is  modi- 
fied very  much  by  the  intensity  of  light  and  the  trans- 
parency of  the  air.     In  the  clear  atmosphere  and  strong 
light  common  in  mountainous  regions,  the  distance  of 
objects  is  apparently  much  diminished. 

When  we  look  at  objects  near  to  us,  the  eyes  are 
rolled  inward,  so  that  the  lines  drawn  through  the 
center  of  each  eye  will  form  a  greater  angle  where  they 
meet  in  the  object,  than  they  would  if  it  were  distant. 
The  muscular  sense  estimates  the  extent  of  this  inclina- 
tion of  the  eyes  toward  each  other,  and  thus  materially 
aids  in  determining  distance. 

174.  Why  Objects  are  seen  Single,  when  an  Image 
is  made  in  each  Eye.  —  When  we  see  objects  with 
two  eyes,   it  is  evident  that  two  distinct  images  are 
formed,   and  yet  the  mind   perceives   but   one    object. 
This  depends  on  our  ability  to  adjust  the  axis  of  vision, 
so  that  the  image  will  occupy  exactly  the  same  point 
on  the  retina  in  each  eye.     Any  thing  that  interferes 
with  the  action  of  the  muscles  which  roll  the  eyeballs, 
or  that  hinders  our  adjusting  the  eyes  to  objects  at  a 
particular  distance,   will   produce  the   phenomenon   of 
double  vision. 

When  we  attempt  to  arrange  three  or  more  objects  at 
different  distances  from  us,  so  that  they  shall  be  in  a 
line,  we  use  but  one  eye,  otherwise  all  the  objects  but 
one  would  be  seen  double.  If  we  press  one  of  our  eyes 


126  PHYSIOLOGY. 

so  as  to  hold  the  ball  firmly  in  the  socket,  we  see  all 
objects  double,  because  we  interfere  with  the  adjustment 
of  the  angle  of  vision. 

175.  The  Advantage  of  two  Eyes.  —  The  advantage 
of  two  eyes  in  seeing  is  not  merely  that  we  double  the 
impression  made  on  the   nervous   center,   but    we    are 
enabled   to   see    more   of  objects   with    two   eyes   than 
with   but   one.      If   we    place    a    card   before   us,  with 
its  edge  directed  to  the   space   between  the    eyes,   we 
will  see  both  sides  of  the  card;  but  if  we  close  one  eye, 
the  side  of  the  card  corresponding  to  that  eye  will  dis- 
appear.    From  this   simple   experiment,   it    is   evident 
that  the  images  in  the  two  eyes  are  not  alike,  but  they 
must  occupy  the  same   point  on  the   retina  to  make 
vision  perfect. 

When  we  look  at  a  plane  surface,  each  eye  has 
exactly  the  same  image  in  it;  but  if  the  surface  is 
irregular,  curved,  or  angular,  each  eye  will  picture 
its  own  side  of  these  irregularities;  but  out  of  the  two 
pictures,  the  mind  perceives  one  perfect  image. 

176.  The   influence   of  the   Mind  on   Vision.  —  In 

cross-eyes,  the  mind  recognizes  the  image  formed  in 
but  one  eye,  and  thus  objects  are  seen  single  which 
otherwise  would  evidently  appear  double.  But  it  is 
true  of  ordinary  vision,  also,  that  the  mind  has  no  per- 
ception of  many  images  that  must  be  formed  on  the 
retina.  Indeed,  the  whole  process  of  sight  is  very 
much  influenced  by  the  mind,  and  often  the  things 
spoken  of  as  objects  of  sight  are  really  the  results 
of  our  judgment  about  the  sensation. 

Distance,  size,  and,  to  a  great  extent,  shape,  are  rather 
complex  judgments  than  simple  sensations.  Another 


VISION.  127 

source  of  false  vision  is,  that  the  image  is  not  perceived 
at  the  instant  it  is  made,  nor  is  its  absence  observed 
the  moment  it  disappears.  The  separate  spokes  of  a 
wheel  in  rapid  motion  blend  together  and  appear  con- 
tinuous. So  if  a  burning  coal  be  whirled  rapidly  in 
a  circle,  it  appears  as  a  continuous  line  of  light,  be- 
cause the  eye  retains  the  first  impression  till  it  is 
reproduced. 

177.  Subjective  Sensation.  —  The  mind  performs  an 
important  part  in  all  our  sensations,  as  well  as  in 
vision.  What  are  commonly  known  as  "delusions  of 
the  senses"  are  really  mental  phenomena  —  morbid 
actions  of  the  perceptive  faculties.  They  are  more 
properly  called  subjective  sensations. 

In  certain  conditions  of  the  skin,  there  is  a  percep- 
tion of  something  creeping  on  the  surface.  In  many 
diseases,  the  patient  is  constantly  harassed  with  certain 
disagreeable  tastes  or  odors.  These  are  perceptions  from 
internal  conditions,  and  not  from  external  impressions 
on  the  organs  of  sense.  Many  persons  are  troubled 
with  perceptions  of  sound,  without  any  external  cause; 
but  the  most  wonderful  exhibition  of  subjective  sensa- 
tion is  to  be  seen  in  patients  laboring  under  de- 
lirium tremens,  when  the  most  frightful  objects  are 
pictured  to  the  mind  with  great  distinctness  and  in 
minute  detail. 

Recapitulation. 

Spherical  aberration,  the  effect  of  enlarging  the  pupil  in  a 
dim  light.  Short-sightedness  may  be  the  effect  of  several 
causes.  Distance  of  an  object  determined  chiefly  by  its  known 
size,  and  the  sharpness  of  its  outline.  Objects  are  seen  singly 


128  PHYSIOLOGY. 

by  the  image  in  each  eye  falling  on  the  same  part  of  each 
retina.  More  of  an  object  can  be  seen  with  two  eyes  than  with 
one.  Vision  is  influenced  by  the  mind.  Certain  conditions  of 
the  brain  produce  false  perceptions,  or  subjective  sensations. 


LESSON   XXII. 

MOTOR    FUNCTION. 

178.  The   Motor  Functions  of  the  Nervous   Sys- 
tem.—  We  have  already  said  (§  120)  that  the  nervous 
system  has  a  three-fold  function ;  or,  rather,  it  performs 
three  distinct  and  nearly  independent  functions.     Sen- 
sation is  but  one  of  these.     By  it  we  become  acquainted 
with  the  external  world,  and  acquire  the  material  for 
thought  —  that  on  which  the  mind  exerts  its  creative 
powers    of    imagination,    comparison,    judgment,    etc. 
Sensation    is  thus    intimately  connected  with   our  ra- 
tional enjoyment ;  but  the  power  of  motion,  communi- 
cated   to    the    muscles   through    the    motor    nerves,    is 
essential  to  life   itself. 

When  the  heart  and  the  respiratory  muscles  cease 
to  move,  death  ensues  instantly.  But  the  motor  func- 
tions have  an  important  bearing  on  the  mental  action. 
While  the  mind  receives  the  thoughts  of  other  minds 
by  the  sentient  nerves,  it  is  able  to  communicate  its 
own  thoughts  only  through  the  motor  nerves. 

179.  Voluntary    and    Involuntary    Movements.  — 

Muscular  motion  has  been  generally  considered  as  of 
two  kinds,  voluntary  and  involuntary ;  or  those  motions 


MOTOR  FUNCTION.  129 

that  are  immediately  under  the  control  of  the  will,  and 
those  over  which  we  are  able  to  exert  little  or  no 
control  by  our  volitions.  The  involuntary  movements 
belong  to  the  functions  immediately  connected  with 
life,  such  as  digestion,  circulation,  secretion,  etc.  Res- 
piration is  a  mixed  function,  controlled  to  a  limited 
extent  by  the  will,  but  beyond  that,  becoming  invol- 
untary. 

The  involuntary  motions  of  the  body,  when  in  a 
healthy  condition,  are  carried  on  without  our  knowl- 
edge, as  well  as  without  our  consent.  We  therefore 
never  feej.  fatigued  from  the  constant  action  of  the 
heart,  or  the  movements  of  the  stomach  during  diges- 
tion. The  wisdom  of  placing  these  important  functions 
beyond  the  reach  of  the  will,  as  well  as  beyond  our 
consciousness,  is  apparent  at  the  first  glance. 

180.  Ganglions  of  Involuntary  Motion. — The  nerves 
supplying  power  to  the  involuntary  muscles,  do  not 
come  directly  from  the  brain  or  spinal  cord,  but  are 
derived  from  a  system  of  ganglions,  or  little  brains, 
located  in  the  vicinity  of  the  great  organs  they  are 
intended  to  supply,  and  these  connect  with  two  nervous 
cords  extending  nearly  the  whole  length  of  the  spinal 
column,  and  occupying  positions  on  each  side  of  it. 
This  double  cord  is  known  as  the  Great  Sympathetic 
nerve.  These  cords  are  really  chains  of  ganglia,  or 
little  knots  of  nervous  matter  arranged  like  the  spinal 
cord,  the  gray  matter  occupying  the  center,  with  the 
white  matter  on  the  surface.  These  ganglia  are  oppo- 
site to  the  space  between  the  vertebra.  They  are  con- 
nected together  by  a  nervous  cord,  and  each  ganglion 
receives  a  filament  from  the  corresponding  spinal  nerve 


130  PHYSIOLOGY. 

at  its  origin,  and  sends  off  branches  which,  uniting 
together,  form  the  ganglia  of  the  involuntary  organs. 

181.  Importance     of     Ganglionic     Nerves.  —  The 

branches  of  this  sympathetic  system  accompany  the 
blood-vessels  even  to  their  capillary  extremities,  and 
seem  to  exert  an  influence  on  those  mysterious  changes 
which  take  place  in  connection  with  this  class  of 
vessels,  such  as  the  secretion  of  fluids  by  certain 
glands,  direct  nutrition  of  the  different  tissues,  etc. 

This  is  demonstrated  by  the  effect  of  injuries  to  the 
branches  of  this  nervous  system  distributed  to  the 
different  organs.  For  instance,  if  the  great  semi-lunar 
ganglion,  from  which  the  diaphragm  derives  its  nerves 
of  involuntary  motion,  be  injured,  breathing  is  so  im- 
paired that  the  patient  frequently  dies  suddenly,  as 
if  from  suffocation.  This  system  has  no  true  sentient 
nerves,  but  certain  mental  emotions  are  referred  to  the 
larger  ganglions,  producing  peculiar  sensations  familiar 
to  every  one. 

182.  Passions   and   Emotions  —  how  expressed.  - 

This  indirect  or  sympathetic  connection  between  the 
mental  condition  and  the  involuntary  organs,  gives 
rise  to  all  the  common  manifestations  of  emotion  or 
passion,  such  as  tears  of  grief,  the  paleness  of  fear,  the 
flush  of  rage,  or  the  blush  of  confusion  or  shame. 
These  being  produced  involuntarily  by  the  several 
mental  conditions  of  which  they  are  the  exponents, 
can  be  artificially  induced  only  by  exciting  in  the 
mind  the  actual  condition  of  which  they  are  the 
proper  representatives. 

The  actor  on  the  stage,  by  the  long  training  of, 
perhaps,  an  originally  active  imagination,  throws  his 


MOTOR   FUNCTION.  131 

mind  into  the  actual  condition  of  that  expressed  in 
the  character  he  is  personating,  and  the  involuntary 
expressions  of  these  conditions  follow,  by  sympathy, 
as  truly  as  if  the  emotions  were  real. 

183.  The  Physiological  Law  of  Sympathy.  —  But 

the  sympathetic  action  does  not  end  here.  Watching 
the  expression  of  the  actor's  emotion,  our  own  minds 
become  similarly  affected,  whether  we  will  it  or  not, 
and  that  condition  is  expressed  by  the  invariable 
action  of  the  involuntary  nerves.  In  this  power  to 
voluntarily  call  up  the  mental  condition  present  in 
the  exercise  of  any  of  the  passions,  and  thus  induce 
the  true  expression  of  the  emotion  through  involuntary 
functions,  consists  the  chief  control  of  the  orator  over 
his  hearers. 

The  speaker  who  can  so  impress  his  own  mind  as  to 
produce  the  mental  state  of  grief,  will  find  the  lachry- 
mal glands  responding  at  once  in  as  copious  a  flow 
of  tears  as  if  his  grief  were  real;  and  his  audience, 
unless  they,  by  a  voluntary  effort,  withdraw  their 
attention,  and  thus  sever  the  cord  of  sympathy,  will 
find  themselves  weeping  too.  Such  are  the  mental 
associations  of  the  involuntary  nerves. 

181.  Degree  of  Sensibility  in  the  Inyoluntary 
Organs.  —  The  organs  which  perform  involuntary  func- 
tions have,  in  their  healthy  condition,  no  sensibility, 
or,  at  least,  they  are  sensitive  only  as  they  are  supplied 
with  nerves  from  the  cerebro-spinal  system.  In  certain 
forms  of  disease,  however,  the  stomach,  intestinal  canal, 
and  heart  become  exceedingly  sensitive  to  the  touch  of 
any  solid  substance. 

Though   the   will  has  no   direct   control   over   these 


132  PHYSIOLOGY. 

functions  yet  the  activity  of  the  voluntary  organs  pro- 
duces a  decided  influence  on  the  rate  and  force  with 
which  they  act.  Brisk  exercise,  short  of  the  point 
of  violence,  and  not  continued  to  fatigue,  will  accel- 
erate all  the  involuntary  actions  in  sympathy  with 
the  voluntary  functions.  If,  however,  the  exercise  be 
violent,  and  be  carried  forward  till  a  sense  of  fatigue 
is  felt,  the  vital  force  will  be  expended  on  the  volun- 
tary organs,  leaving  the  involuntary  functions  in  an 
impaired  condition. 

185.  Effect  of  Sleep.  —  This  sympathy  of  the  invol- 
untary with  the  voluntary  movements  of  the  body  is 
furtffer  seen  in  the  diminished  force  and  activity  of 
circulation,  digestion,  and  secretion  during  sleep,  which, 
as  we  shall  see  in  the  proper  place,  is  a  suspension  of 
the  voluntary  functions. 

Though  the  involuntary  muscles  are  not  capable  of 
feeling  fatigued,  yet  they  are  subject,  at  least  in  some 
degree,  to  the  rapid  exhaustion  which  so  soon  succeeds 
to  the  forcible  contraction  of  a  voluntary  muscle. 
Though  the  heart  may  continue  to  perform  its  function 
incessantly  for  its  "three  score  and  ten"  years,  yet  we 
must  remember  that  its  intervals  of  relaxation  are 
equal  to  its  periods  of  contraction;  in  other  words, 
the  heart  rests  half  its  time. 


Recapitulation. 

» 

The  motor  functions  are  essential  to  the  maintenance  of  life. 
Muscular  motions  are  of  two  kinds,  voluntary  and  involuntary. 
The  cranial  and  spinal  nerves  govern  voluntary  motion.  In- 
voluntary movements  are  connected  with  the  brain  through 


NERVOUS  FUNCTIONS. 


133 


ganglions.  The  sympathetic  nerve,  with  its  connected  ganglions, 
controls  the  circulation,  secretion,  etc.  Passions  and  emotions 
are  expressed  through  the  sympathetic  nerve.  Voluntary  mo- 
tions effect  involuntary  functions  indirectly. 


LESSON    XXIII. 


FIG.  71.— TRANSVERSE 
SECTION  OF  THE 
SPINAL  CORD. 


NERVOUS   FUNCTIONS. 

186.  Special  Functions  of  the  Spinal  Cord.  — In 

the  anatomical  description  of  the  brain  and  spinal  cord, 
it  was  observed  that  the  proportion  of  gray  matter, 
compared  with  the  white,  was  smaller  in  the  cord  than 
in  either  the  cerebrum  or  cerebel- 
lum. As  we  come  now  to  inquire 
into  the  motor  function  of  the 
spinal  cord,  it  will  be  well  to  note 
'°  the  relative  position  of  these  two 
substances.  As  is  shown  in  the 
subjoined  figure,  the  gray  matter 
occupies  the  center  of  the  cord, 
and  is  nearly  surrounded  by  the 
white  substance. 

Both  roots  of  the  spinal  nerves 
communicate  first  with  the  white 
matter  of  the  cord,  but  do  not  ter- 
minate there.  JMany  of  their  fila- 
ments dip  downward  through  the  external  white  en- 
velope of  the  cord,  and  terminate  on  the  gray  matter  at 
its  center.  This  arrangement  gives  to  the  cord  a  two- 
fold function :  1st.  It  is,  by  its  white  matter,  a  part  of 


«.  Anterior  fissure,  b. 
Posterior  fissure,  c, 
c.  Gray  matter. 


134  PHYSIOLOGY. 

the  continuous  chain  of  communication  between  the 
gray  substance  of  the  brain  and  the  motor  and  sentient 
extremities  of  the  nerves;  and,  2d.  Under  certain  cir- 
cumstances, it  assumes  the  functions  of  brain  proper, 
and  carries  forward  its  actions  unconsciously. 

187.  Complex  Nature  of  Voluntary  Motion. — Vol- 
untary motion,  however  simple  it  may  appear,  is  a  very 
complicated   matter.     If  the   hand   comes    into  contact 
with  a  hot  poker,  an  impression  is  made  on  the  extremi- 
ties of  the  sentient  nerves;  this  is  immediately  trans- 
mitted to  the  spinal  cord  by  the  brachial  nerve,  and, 
through  the  white  matter  of  the  cord,  is  conveyed  to 
the  gray  substance  of  the  brain,  where  the  sense  of  heat 
is  perceived,  and  immediately  an  impulse  is  transmitted 
to  the  proper  motor  nerves  by  the  same  route  through 
the  spinal  cord,  the  appropriate  muscles  are  called  into 
action,  and  the  hand  removed  from  its  dangerous  con- 
tact with  a  hot  surface.     That  these  actions  take  place 
consecutively  can  be   clearly  demonstrated  by  experi- 
ment, and  yet  the  touch,  the  sensation,  and  the  motion 
appear  to  occur  at  the  same  instant. 

188.  Reflex  Motions  originate  in  the  Spinal  Cord. — 

But  the  greater  number  of  voluntary  motions  do  not 
originate  directly  from  sensations  transmitted  to  the 
brain,  but  spring  from  independent  volitions.  A  vol- 
untary motion,  which  at  first  requires  a  specific  action 
of  the  brain  and  a  clear  consciousness  of  the  volition 
which  produced  it,  will,  after  being  often  repeated, 
become  habitual,  and  be  produced  without  any  con- 
sciousness .of  the  volition  commanding  it. 

These  are  called  reflex  motions,  and  are  supposed  to 
originate  in  the  gray  matter  of  the  spinal  cord,  which, 


NERVOUS  FUNCTIONS.  135 

in  these  instances,  performs  the  true  functions  of  brain 
without  our  being  conscious  of  its  action.  A  great 
majority  of  the  movements  of  the  body  belong  to  this 
class  of  reflex  or  unconscious  action. 

189.  Unconscious    nature    of   Reflex    Motions.  - 

Movements  thus  performed  fatigue  us  much  less,  and 
are  usually  performed  with  greater  accuracy,  than  those 
which  demand  our  conscious  attention  to  every  volition 
and  every  motion  resulting  therefrom.  In  illustration 
of  this,  take  the  example  of  a  walk.  At  every  step  the 
foot  is  carried  forward  by  the  contraction  of  a  great 
number  of  muscles ;  but  the  attention  is  diverted  to  the 
scenery  around  us,  or  to  the  particular  objects  along  our 
pathway ;  or,  if  not  to  these,  the  mind  is  engaged  with 
some  train  of  thought,  or  in  the  solution  of  some 
abstract  problem,  and  at  the  end  of  our  walk  we  are 
unable  to  recall  the  volition  which  produced  any  one 
of  the  thousands  of  separate  motions  we  have  made,  or 
the  consciousness  of  a  single  step  we  have  taken. 

190.  Reflex  Motions  less  exhaustive  than  Volun- 
tary ones.  —  When  we  begin  a  kind  of  work  to  which 
we  are  not  accustomed,  our  motions  are  awkward  and 
clumsy,   and   each    movement   requires   our   undivided 
attention.     They  are   cerebral   motions.     But  after  we 
establish  the  habit  of  these  motions,  however  complex 
they  may  be  —  or,   in  common   phrase,   after   we  have 
acquired    the    handicraft  —  the    movements    are    made 
gracefully,    with   ease,   and   without    our    attention    or 
consciousness.     These  are  spinal  or  reflex  actions. 

It   is  a  matter  of  common  observation,  that  a  kind 
of  labor  to  which  we  are  not  accustomed,  fatigues  us 

more  than  heavier  labor  to  which  we  have  habituated 
B.  P.— 12. 


136  .         PHYSIOLOGY. 

ourselves.  This  is  because  cerebral  action  is  more  ex- 
hausting than  spinal  or  reflex  action. 

191.  How   the   Nerves   convey   Impressions.  —  We 

have  spoken  of  the  impressions  made  on  the  looped 
extremity  of  a  sentient  nerve,  and  of  their  communi- 
cation along  that  nerve  to  the  seat  of  perception  in  the 
brain,  and  of  the  transmission  of  a4i  impulse  or  force 
from  the  same  center  of  influence,  along  the  motor 
nerves  to  the  muscles  to  produce  motion ;  but  our  closest 
scrutiny  does  not  detect  any  matter,  however  subtle,  as 
traversing  the  nerves  in  either  direction. 

The  nervous  tissue,  like  other  tissues  of  the  body,  is 
made  of  cells,  and  those  in  the  white  matter  of  the 
brain,  and  in  the  nervous  cords,  are  elongated  into 
tubuli,  and  what  is  transmitted  is  probably  the  mere 
motion  or  undulation  of  the  molecules  of  which  these 
tubuli  are  formed. 

192.  Communication  with  the  Brain  essential  to 
Sensation  or  Motion.  —  A  continuity  of  nerve  structure 
from  the  brain  to  the  muscles  of  motion,  and  from  the 
organs  of  sensation  to  the  brain,  is  absolutely  essential 
to  motion  or  sensation.    If  the  nerve  be  divided,  or  if  the 
communication  with  the  brain  through  the  spinal  cord 
be  broken,  all  the  organs  to  which  that  nerve  is  distrib- 
uted will  lose  the  power  of  either  sensation  or  motion. 

From  the  fact  that  the  spinal  nerves  originate  by 
separate  roots  from  different  tracts  of  the  spinal  cord, 
(§  122,)  and  these  roots  each  performs  a  different  func- 
tion, it  is  possible  to  lose  the  power  of  feeling  in  a  part 
while  the  function  of  motion  remains  unimpaired, 
and  the  reverse.  Both  the  power  of  motion  and  sensa- 
tion may  be  lost  in  a  limb,  while  the  circulation  in  it 


NERVOUS  FUNCTIONS.  137 

will  be  scarcely  disturbed,  this  being  under  the  control 
of  the  ganglionic  nerves. 

193.  Effect  of  Injury  to  the  Nervous  Trunks.  — If 

the  trunk  of  a  nerve,  at  any  point  between  its  origin 
and  its  sentient  extremity,  be  irritated  or  injured  in 
any  way,  the  pain  will  be  referred  to  the  part  on  which 
the  sentient  extremities  of  the  nerve  are  spread.  When 
a  limb  has  been  amputated,  and  the  ends  of  the  divided 
nerves  left  in  a  condition  exposing  them  to  injury  from 
compression  or  irritation,  the  patient  will  complain  of 
pain  in  the  lost  limb;  and  these  unpleasant  sensations 
will  frequently  continue  for  years.  The  practical  lesson 
to  be  learned  from  this  is,  that  sensation  is  not  to  be 
received  as  infallible  evidence  that  the  cause  producing 
it  is  located  at  the  point  where  it  is  felt.  It  may  be  at 
any  point  along  the  trunk  of  the  nerve. 

194.  Motions   Classified.  —  The   motor   functions   of 
the  nervous  system  may  be  arranged  in  three  classes : 
1st.  Those  motions  which  originate  in  the  gray  matter 
of  the  brain,  and  proceed  from  a  conscious  impulse  of 
the  will;   2d.  Those  which   at  first  are  voluntary  and 
conscious,  but  by  frequent  repetition  come  to  be   per- 
formed unconsciously,  under  the  control  of  the  spinal 
cord;   3d.  Those  which  are  purely  involuntary,  and  of 
which    we    are    entirely   unconscious.     These    motions 
originate  in  the  ganglions,  and  the  organs  thus  acting 
are  supplied  chiefly  with  nerves  from  this  source. 

Recapitulation. 

The  spinal  cord  consists,  like  the  brain,  of  gray  and  white 
matter,  but  their  relative  positions  are  inverted.  Voluntary 
motions  are  complex.  Reflex  motions  originate  in  the  spinal 


138  PHYSIOLOGY. 

cord.  They  are  performed  unconsciously,  and  are  less  fatigu- 
ing than  motions  of  cerebral  origin.  Sensation  and  motion  re- 
quire unbroken  nervous  connection  with  the  brain.  Injuries 
of  nervous  trunks  produce  sensation  which  is  referred  to  the 
extremities. 


LESSON    XXIV. 

MENTAL    FUNCTION. 

195.  Thought  —  dependent    on    the   Brain,  —  The 

third  function  of  the  brain  is  thought.  In  what 
manner  the  brain  acts  when  one  thinks,  we  may, 
perhaps,  never  know;  and  yet  we  are  as  certain  that 
it  is  the  instrument  of  thought,  as  we  know  its  con- 
nection with  sensation  and  motion.  Compression  of 
the  brain  suspends  consciousness  and  thought,  as  cer- 
tainly as  compression  of  the  spinal  cord  arrests  motion, 
and  destroys  sensation  in  the  parts  beyond  the  com- 
pression. 

Certain  diseased  conditions  of  the  brain  derange  the 
function  of  thought,  and  produce  the  different  forms 
and  grades  of  insanity  corresponding  to  the  character 
and  intensity  of  the  disease.  Malformation  of  the  brain 
may  be  regarded  as  a  constant  accompaniment  of  idiocy; 
and,  as  a  general  rule,  the  extent  of  the  malformation 
measures  the  loss  of  mental  power. 

196.  Development  of  Brain  measures  Thought.— 

To  suppose  that  the  power  of  thought  belongs  alone 
to  the  human  race  is,  perhaps,  the  most  common 
mistake  on  this  subject.  There  is  unmistakable  evi- 


MENTAL    FUNCTION.  139 

dence  that  the  inferior  animals  think,  and  that  in 
them  the  power  of  thought  is  more  or  less  perfect, 
according  to  the  degree  of  brain  development. 

In  the  vertebrate  animals,  as  we  ascend  the  scale 
from  fishes  to  reptiles,  from  reptiles  to  birds,  from  birds 
to  mammals,  and  finally  to  man,  we  find  at  every  step 
an  advance  in  the  perfection  of  the  nervous  system; 
but  this  advance  affects  chiefly  the  cerebrum.  Fishes 
have  a  very  perfect  spinal  cord,  the  rudiments  of  a 
cerebellum,  but  nothing  that  deserves  to  be  called  a 
cerebrum.  With  them,  thought  is  little  more  than  an 
instinct  of  self-preservation.  In  reptiles,  the  cerebrum, 
though  very  small,  can  be  clearly  distinguished;  and 
so  the  advance  continues,  intelligence  keeping  pace 
with  it,  till  it  culminates  in  man. 

197.  The  Cerebrum,  the  Organ  of  Thought.  —  But 

even  in  the  mammalia,  the  class  to  which  man,  as  an 
animal,  belongs,  the  proportion  of  the  c'erebrum  to  the 
cerebellum  varies  very  much.  In  the  lower  orders  of 
this  class,  such  as  the  sloth,  the  ant-eater,  and  the 
opossum,  the  cerebrum  is  but  little  larger  than  the 
cerebellum ;  but,  in  man,  it  is  from  seven  to  ten  times 
as  large.  This  fact  has  led  physiologists  to  infer  that 
the  cerebrum  is  the  proper  organ  of  thought,  and  the 
inference  is  probably  well  founded. 

There  is  another  feature  in  which  the  human  brain 
differs  from  that  organ  in  inferior  animals.  The  pro- 
portion of  gray  matter  is  much  greater  in  the  brain  of 
man  than  in  that  of  any  of  the  lower  animals.  But 
here,  again,  we  find  an  ascending  scale  corresponding 
to  the  degree  of  intelligence  in  the  animal.  This  is  so 
uniform,  that  it  may  be  regarded  as  establishing  a 


140  PHYSIOLOGY. 

general  rule,  that  the  proportion  of  gray,  as  compared 
with  the  white  matter  in  the  cerebrum,  measures  the 
sagacity  of  the  animal. 

198.  Voluntary  and  Involuntary  Thought. — Within 
certain  limits,  thought  is  an  involuntary  function,  but 
beyond  these,  the  intellectual  phenomena  appear  to  be, 
to  a  great  extent  at  least,  under  the  control  of  the  will. 
Thoughts   which    arise,  immediately   from    impressions 
made  through  the  senses  are  not  voluntary,  but  appear 
to   spring   up   spontaneously.     Another  source  of  invol- 
untary thought  is  found  in  the  appetites  and  desires 
connected  with   the    maintenance    of  life   and   health, 
such   as   hunger   and   thirst. 

In  the  higher  and  more  purely  intellectual  regions 
of  thought,  the  will  exercises  at  least  a  directive  power 
over  the  mental  action,  selecting  the  subject  of  thought, 
and  determining  the  direction  of  the  investigation,  and 
how  far  it  shall  be  prosecuted. 

199.  Voluntary  Thought  modified  by  Training.— 

The  power  to  maintain  complete  control  of  the  mental 
functions  varies  materially  in  different  individuals. 
To  some  extent  this  variation  is  natural,  but  to  a 
great  extent  it  is  the  result  of  training  and  edu- 
cation. Every  student  has  observed  how  much  more 
readily  and  perfectly  he  can  command  his  attention 
to  the  subject  of  his  studies,  after  his  mind  has 
been  trained  for  years  in  the  daily  business  of  study, 
than  he  could  when  he  first  made  his  acquaintance 
with  books. 

The  relation  existing  between  the  voluntaiy  and  in- 
voluntary departments  of  thought,  gives  rise  to  many 
curious  and  interesting  phenomena.  The  power  to 


MENTAL   FUNCTION.  141 

concentrate  the  thoughts  by  a  voluntary  effort,  and  fix 
them  on  any  line  of  investigation,  is  often  so  strong  as 
to  completely  suppress  the  involuntary  powers  for  the 
time  being.  This  in  common  language  is  called  absent- 
mindedness.  It  may  arise  from  the  great  force  of  the 
directive  faculty,  or  from  the  feeble  effect  of  the  sentient 
power  on  the  brain. 

200.  Life  in  the  Ascending  Scale.— Modern  phi- 
losophy assumes  that  motion,  every- where  in  this  world, 
is  the  result  of  force,  operating  on  and  through  matter. 
Gravity,    the   chemical,    electrical,  and   thermal    forces 
pervade    the    entire    material    world.      In    addition   to 
these,  we  find  the  force  of  organic  life  manifesting  its 
presence  in  the  vegetable  world  by  the  phenomena  of 
nutrition,  and  through  the  mysterious  process  of  cell 
growth,  molding  each   individual  into  a  specific  form. 
Superadded  to  this,  we  have  animal  life  manifested  in 
the  three-fold  function  of  the  nervous  system  —  sensa- 
tion,   voluntary   motion,    and    thought.     Besides    these 
phenomena,  man   also   possesses  the   power  of  abstract 
thought,  giving  him  the  faculties  of  imagination,  moral 
and  religious  perceptions,  etc. 

201.  The    Human    Powers.  —  In  the   possession  of 
these   human    powers,  man  differs  from  all  the  lower 
animals   as   really   as   they  differ   from   the    vegetable 
world.     As  the  formation  of  cells  and  the  construction 
of  organs,  etc.,  are  functions  of  organic  life,  and  sensa- 
tion, motion,  and  thought  are  functions  of  animal  life, 
so  abstract   reasoning,   moral   sensibility,    the   creative 
faculty  of   imagination,   with    all    its   high    powers  of 
examining  and  comparing   things   which    are    not,  as 
though   they  were,  are  functions  of  spirit. 


142  PHYSIOLOGY. 

As  animal  life  differs  from  the  organic,  not  in  degree 
merely,  but  also  in  kind,  so  the  power  of  abstract  reason 
differs  from  animal  sensation  and  intellection  —  it  is  of 
another  kind.  Man  manifests  all  the  life  forces  of  the 
vegetable  and  animal  worlds,  and  in  addition  to  these, 
functions  which  belong  to  a  higher  force,  which  we 
call  Spirit. 

202.  Man,  compared  with  the  Lower  Animals.— 

Of  the  nature  of  any  force,  abstractly,  we  know  nothing. 
Its  existence,  and  the  law  governing  its  activities,  we 
know  only  by  a  careful  study  of  what  it  does.  The 
lower  animals  have  all  our  senses,  and  some  of  these  are 
much  more  acute  than  in  man.  They  have  memory, 
in  some  instances  amazingly  perfect;  they  manifest 
emotions  and  desires ;  and  to  gratify  these  desires,  they 
adopt  means  to  that  end,  limiting  their  reasoning  to 
objects  of  sensation,  however,  and  circumscribing  their 
efforts  to  the  securing  of  pleasurable  emotions,  and  the 
avoidance  of  painful  sensations.  But  they  manifest  no 
power  to  separate  and  examine,  abstractly,  the  qualities 
of  either  actions  or  objects.  These  are  functions  of  the 
spirit,  and  in  the  exercise  of  these  powers  man  is  a 
moral  agent :  he  knows  right  and  wrong ;  has  a  con- 
science, and  feels  his  accountability,  and  is,  therefore,  a 
religious  being;  he  reasons  on  form  and  number  as 
abstract  qualities  of  things,  and  is,  therefore,  a  mathe- 
matical being.  These  are  attributes  of  spirit. 

Recapitulation. 

Thought  is  a  function  of  brain.  This  facujty  is  not  confined 
to  man,  but  is  manifested  in  the  lower  animals  in  proportion 
to  brain  development.  The  cerebrum  is  probably  the  organ 


SLEEP.  143 

of  thought.  The  sagacity  of  animals  may  be  measured  by  the 
proportion  of  gray  matter  in  the  cerebrum.  Thought  is  an  in- 
voluntary function,  but  the  directive  power  is  voluntary. 

Abstract  thoughts,  such  as  relate  to  the  moral  qualities  of 
actions,  the  mathematical  properties,  form,  number,  etc.,  are 
functions  of  spirit,  and  belong  exclusively  to  man. 


LESSON   XXV. 

SLEEP. 

203.  Sleep,  as  it  affects  the  Yital  Functions.  — The 

constant  activity  of  the  brain,  in  its  triple  function, 
rapidly  exhausts  its  power,  and,  like  other  living 
organs,  it  requires  rest.  But  the  rest  of  the  brain, 
necessary  to  restore  its  wasted  energies,  like  rest  in 
other  organs,  is  the  suspension  of  its  function.  To 
suspend  the  functions  of  the  nervous  system,  is  to 
induce  a  state  of  entire  unconsciousness.  This  is  sleep, 
and  is  a  necessity  in  all  animals,  as  well  as  in  man. 

It  is  proper  to  say,  however,  that  the  complete 
suspension  of  function  does  not  extend  to  the  whole 
nervous  system.  It  begins  with  and  belongs  properly 
to  the  cranial  brain,  extending,  by  a  kind  of  secondary 
influence,  to  the  spinal  cord,  and  modifying  but  slightly 
the  great  sympathetic  nerve  and  its  ganglions.  There- 
fore, all  the  involuntary  movements  of  the  body  con- 
tinue during  sleep,  but  they  are  performed  more  slowly 
and  with  less  force. 

204.  The  order  in  which  Sleep  affects  the  Senses.— 

The    transition    from   a   waking   to    a    sleeping    state, 

though   often    very   rapid,    is   a   process   consisting   of 
B.  P.— 13. 


144  PHYSIOLOGY. 

several  consecutive  steps.  The  progress  toward  a  state 
of  sleep  appears  to  begin  with  impaired  sensation,  the 
senses  of  smell  and  taste  being  first  to  feel  the  effect; 
after  this  the  eyes  close,  and  vision  ceases.  The  sense 
of  touch  is  early  impaired,  but  does  not  entirely  dis- 
appear until  all  the  other  faculties  are  locked  in  sleep. 

The  sense  of  hearing  maintains  its  function  unim- 
paired as  long  as  consciousness  remains;  and  there  are 
good  reasons  to  believe  that,  though  unconscious  of  it, 
the  auditory  sense  is  constantly  reporting  to  the  per- 
ceptive center,  though  no  notice  may  be  taken  of  these 
reports.  A  man  falls  asleep  in  the  middle  of  a  sermon, 
but  as  soon  as  the  voice  ceases  he  wakes,  from  the 
auditory  nerve  ceasing  to  report  to  the  perceptive 
center. 

205.  Cerebral  and  Spinal  Functions  differently 
influenced.  —  While  sleep  is  thus  stealing  on  our 
senses,  the  power  of  voluntary  motion  is  early  sus- 
pended, especially  those  motions  which  demand  the 
attention,  and  which  requires  each  a  special  volition 
for  its  performance.  The  habitual  motions,  or  those 
which  are  performed  by  the  reflex  action  of  the  spinal 
cord,  are  continued  longer,  sometimes  even  after  con- 
sciousness is  entirely  suspended,  as  in  case  of  persons 
walking. 

Somnambulism,  or  sleep-walking,  is  but  the  waking 
state  of  the  functions  under  the  influence  of  the  reflex 
action  of  the  spinal  cord.  The  involuntary  functions, 
such  as  respiration,  circulation,  digestion,  etc.,  as  soon 
as  the  voluntary  movements  of  the  body  are  suspended, 
feel  the  effect  at  once.  The  breathing  is  not  so  deep, 
and  the  number  of .  inspirations  in  a  given  time  is 


SLEEP.  145 

reduced;  the  pulse  is  generally  diminished  in  fre- 
quency and  force,  and  the  temperature  of  the  body  falls 
sensibly. 

206.  Effect  of  Sleep  on  the  Mental  Faculties.- 

In  the  mental  department  of  brain  action,  sleep  first 
impairs  the  directive  power  of  the  mind.  By  this  we 
mean  the  faculty  which  determines  the  course  which 
our-thoughts  shall  pursue.  Next  follow  the  powers  of 
abstract  reasoning,  imagination,  and  memory ;  and  last 
of  all,  the  mind  ceases  to  respond  to  the  impressions 
made  on  the  senses,  and  consciousness  of  our  person- 
ality, or  even  existence,  is  lost. 

Just  before  consciousness  becomes  extinct,  there  some- 
times supervenes  a  curious  intermediate  state,  which  in 
common  language  is  called  dozing.  We  are  still  con- 
scious, but  unable  to  discriminate  between  impressions 
made  by  external  objects  through  the  senses,  and  those 
made  from  within  by  our  own  thoughts.  This  state  is 
near  akin  to  dreaming. 

207.  Sleep  is  Brain  rest.  — In  a  healthy  state  of  the 
body,  after  about  fifteen  hours,  more  or  less,  spent  in 
brain   activity,   the    nervous   system   demands   rest,  to 
recuperate  its  powers  and  restore   its  exhausted  ener- 
gies.    Sleep  is  the  only  true  brain  rest.     We  can  tem- 
porarily repair  an  exhausted  faculty  by  suspending  its 
action,  or  exchanging  it  for  some  other  form  of  brain 
activity;    as,  for  example,  when   fatigued  with  study, 
we  take  a  brisk  walk,  thus  transferring  the  action  to 
the  motor  nerves;  yet  the  brain,  as  a  whole,  is  suffering 
an  exhaustion  of  its  force,  which  can  be  restored  only 
by  sleep. 

We  may,  by  a  voluntary  effort,  postpone  from  hour  to 


146  PHYSIOLOGY. 

hour  the  demanded  rest,  but,  finally,  it  supervenes 
involuntarily,  or  inflammation  of  the  brain  will  ensue. 
Well  authenticated  instances  are  on  record  of  persons 
falling  asleep  on  the  battle-field,  or  in  the  midst  of  a 
terrible  storm  at  sea,  the  presence  of  death  itself  not 
being  able  to  keep  them  awake. 

208.  How  much  Sleep  is  Necessary.  —  The  demand 
for  sleep  differs  materially  in  different  persons.     Chil- 
dren require  more  hours  of  sleep  than  do  adults,  and 
their  sleep  is  more  profound,  and  the  suspension  of  all 
the  brain  functions  is  more  perfect.     As  a  general  rule, 
women  endure  loss  of  sleep  better  than  men,  and  the 
nervous  better  than  sanguine  or   lymphatic   tempera- 
ments. 

Of  the  three  functions  of  brain,  the  mental  is  the 
most  exhaustive.  Next  to  this  stands  the  function 
of  sensation;  and  that  which  demands  the  least  sleep 
is  the  motor  function;  or  muscular  activity.  No  rule 
can  be  laid  down,  with  any  degree  of  certainty,  pre- 
scribing a  given  number  of  hours  for  sleep  in  the 
twenty-four.  Age,  sex,  temperament,  kind  of  employ- 
ment, condition  of  health,  etc.,  will  materially  modify 
any  rule  we  may  adopt. 

209.  How  far  Sleep  is  Toluntary.  —  Though  sleep 
can  not  be  voluntarily  induced,  yet  we  may  place  our- 
selves in  such  a  condition  that  it  will  be  invited,  and 
will   almost    invariably  supervene.     Silence,    darkness, 
and  the  absence  of  any  object  of  sense,  together  with 
a  state  of  muscular  repose,  will  place  the  brain  in  a 
condition  where  no  external  demand  on  its  powers  can 
be  made.     In  this  state  of  repose,  it  falls  very  naturally 
into  unconscious  sleep,  unless  this  is  prevented  by  the 


SLEEP.  147 

activity  of  the  representative  faculties,  or  the  creative 
powers  of  the  imagination.  These,  in  persons  of  active 
minds,  often  become  troublesome,  inducing  a  state  of 
wakefulness  which  is  always  exhaustive  of  the  vital 
force,  and  sometimes  causes  dangerous  disease  of  the 
brain. 

210.  Coma  — how  it  differs  from  Sleep.  — Coma  is 
a  condition  of  the  brain  which,  in  its  external  mani- 
festations, resembles  very  much  a  profound  sleep.  But 
in  this  state,  consciousness  can  not  be  restored  by  or 
through  impressions  made  on  the  organs  of  sense. 
Natural  sleep  may  be  regarded  as  an  objective  condition; 
one  by  one  the  senses  suspend  their  functions,  and  cut 
the  brain  off  from  the  external  world,  and  thus  se- 
cluded, it  sinks  into  a  state  of  insensibility.  In  coma, 
the  brain  suffers  from  mechanical  compression,  from  an 
engorged  state  of  its  blood-vessels,  from  the  presence  of 
alcohol  or  some  other  narcotic,  till  unconsciousness 
supervenes,  and  impressions  made  through  the  senses 
can  no  longer  arouse  it  to  action.  It  is  in  a  state  of 
subjective  sleep. 

Recapitulation. 

Sleep  is  brain  rest,  and  is  common  to  all  animals.  It  affects 
the  involuntary  functions  only  indirectly.  Sleep  approaches  by 
successive  steps,  affecting  the  senses  in  a  regular  order. 

Somnambulism  is  the  waking  state  of  the  spinal  cord  in  its 
reflex  functions.  Of  the  mental  faculties,  the  directive  power 
first  sleeps,  and  afterward  the  power  to  perceive  sensations, 
etc.  Sleep  is  involuntary,  but  may  be  invited  or  repelled  by 
circumstances.  Sleep  is  an  objective  condition.  Coma  is  sub- 
jective sleep. 


PART   II. 

HYGIENE 


LESSON  XXVI. 

HEALTH. 

211.  Hygiene  defined — the  Importance  of  Health. — 

The  art  of  preserving  health  is  merely  the  application 
of  correct  physiological  principles  to  our  daily  life. 
As  we  have  seen,  the  human  body  in  living  action  is 
a  very  complex  piece  of  machinery.  Though  wisely 
contrived  and  admirably  constructed  for  the  perform- 
ance of  its  very  complicated  functions,  yet  it  is  liable 
to  derangements  both  of  structure  and  force. 

The  causes  leading  to  these  derangements,  and  the 
circumstances  under  which  they  occur,  and  the  mode 
of  preventing  their  occurrence,  constitute  the  science 
of  Hygiene ;  and  its  correlate  art  is  the  observance 
of  such  rules  of  life  as  will  most  effectually  avoid  the 
causes  of  derangement  and  disease.  The  importance 
of  this  knowledge  in  practice  is  so  obvious  to  all, 

(149) 


150  HYGIENE. 

that  not  one  word  is  necessary  on  that  subject.  With- 
out good  health,  there  is  neither  enjoyment  or  profit 
in  life ;  therefore,  to  secure  good  health  is  the  first  duty 
of  every  human  being;  nor  can  we  neglect  this  duty 
without  incurring  a  fearful  responsibility. 

212.  Relation  of  Physiology  to  Hygiene.  —  In  the 

first  part  of  these  lessons  we  attempted  to  give  the 
student  a  correct  idea  of  the  form  and  structure  of  the 
several  organs  of  the  human  body,  and  their  action  in 
a  normal  or  healthy  condition.  This  knowledge  has 
two  important  practical  applications :  the  first  of  these 
is  to  preserve  health  while  we  have  it;  the  second  is. 
to  restore  it  when  it  is  lost. 

If  by  accident,  neglect,  or  violation  of  the  physio- 
logical conditions  of  vital  actions,  whether  from  ig- 
norance or  willful  inattention,  these  actions  are  im- 
paired, deranged,  or  disturbed,  great  skill  and  knowl- 
edge are  required  in  the  physician,  in  order  to  restore 
them  to  the  normal  condition;  but  the  knowledge  and 
observance  of  a  few  simple  laws  constitute  the  art  of 
maintaining  health,  and  these  are  within  the  reach  of 
all. 

213.  False  Ideas  of  Disease  —  their  Influence  on 
Health.  —  The  study  and  practice  of  hygiene  has  been 
very  much  impeded  by  false  notions  of  the  nature  of 
disease.     In   ancient   times,   diseases   were   regarded   as 
the  inflictions  of  malignant  spirits,  who   entered  into 
the  living  body,  deranged  the  delicate  machinery,  and 
disturbed  its  harmonious  action.     This  superstition  has 
long  since  been  dispelled  by  the  light  of  science,  but 
there    lingers    still,    in    the    common    mind,    the    error 
which   supposes  that  disease  is  a  thing  —  an  undefined 


I 


HEALTH   AND  DISEASE.  151 

and  indefinable  something — which  has  somehow  gained 
a  lodgment  in  the  body,  and  is  to  be  driven  out  by 
medicines.  Such  notions  as  these  are  very  unfavorable 
to  the  introduction  of  healthful  observances  in  our  daily 
life.  When  the  mind  has  once  fully  settled  in  the  con- 
clusion that  disease  occurs  by  a  kind  of  fatal  necessity, 
which  no  precautions  can  avail  to  prevent,  and  all  that 
remains  is  for  the  physician  to  find  some  specific  which 
has  the  mysterious  power  of  expelling  it,  but  little  care 
will  be  taken  to  prevent  it. 

214.  Health  and  Disease  defined.  —  From  a  careful 
study  of  the  living  body,  we  learn  that  vital  force,  if 
not   resulting   from   chemical   change,   is,   at  least,  its 
constant    accompaniment;    and   the   development    and 
maintenance   of  animal   power  are  dependent   on   vital 
transformations.     The    lungs    are    in    constatit    action, 
supplying  oxygen  to  the  blood;   and  the  heart  keeps 
that   blood  in  incessant  motion  through  all  the  parts 
of  the  body.     But  these   sensible   and   visible   motions 
are  only  accessory  to  the  chemical  changes  effected  by 
the  oxygen  thus  transmitted. 

These  changes  take  place  in  the  tissues  of  the  body, 
and  in  the  combustible  elements  of  our  food,  evolving 
from  the  change  both  heat  and  vital  force.  This  active 
change  and  constant  renewal  of  the  particles  consti- 
tuting the  body,  is  HEALTH;  the  disturbance,  obstruc- 
tion, or  perversion  of  this  transformation  of  the  tissues, 
or  the  imperfect  elimination  of  its  products,  is  DISEASE. 
It  is  not  a  malignant  entity,  but  a  morbid  action. 

215.  Diminished  Transformation,  a  diseased  con- 
dition.—  A  disease  may,  however,  consist  in  diminished 
or  suspended  action,  as  well  as  in  its  perversion.     In 


152  HYGIENE. 

all  diseases  of  debility,  the  transformation  of  the  tissues 
takes  place  too  slowly;  and  nutrition,  in  all  its  pro- 
cesses, from  the  first  action  of  the  mouth  on  the  food 
to  its  final  deposition,  is  impaired,  resulting  in  prostra- 
tion of  all  the  vital  forces,  and  general  emaciation  of 
the  body. 

On  the  other  hand,  in  febrile  diseases  the  tissues 
are  rapidly  transformed,  and  the  force  evolved  from 
this  change  appears  in  the  correlate  form  of  heat, 
while  the  tissues  thus  wasted  are  not  replaced,  as 
nutrition  is  almost  entirely  suspended.  All  narcotic 
substances,  such  as  tobacco,  opium,  alcohol,  etc.,  pro- 
duce a  really  diseased  condition,  inasmuch  as  they 
diminish  the  amount  of  chemical  change  in  the  system 
in  a  given  time.  Quinine,  iron,  and  kindred  sub- 
stances, though  they  disturb  the  normal  rate  of  vital 
action  by  increasing  the  amount  of  change,  can  hardly 
be  said  to  produce  disease,  as  the  nutrition  is  aug- 
mented in  the  same  proportion. 

216.  Disease  from  Perverted  Action.  —  But  disease 
may  consist  in  a  perverted  chemistry  of  the  body, 
resulting  in  the  formation  of  compounds  not  found 
in  the  healthy  state  of  the  system.  Such  are  the 
concretions  found  in  and  about  the  joints  in  gout,  the 
gall-stones  found  in  the  gall-bladder  under  certain  cir- 
cumstances, and  the  gravel  found  in  the  urinary  organs. 
But  whatever  may  be  the  characteristics  of  disease,  it 
will  be  found  to  consist  in  diminished,  accelerated,  or 
perverted  action,  in  reference  to  the  chemical  change 
going  on  in  the  living  body. 

The  disturbing  causes,  which  thus  derange  the  vital 
action,  may  not  always  be  within  the  reach  of  human 


DURATION  OF  LIFE.  153 

knowledge,  or,  if  known,  may  not  be  under  our  con- 
trol, yet,  in  a  great  majority  of  cases,  we  can  discover 
and  avoid  the  course  of  life  inducing  these  derange- 
ments, and  thus  escape  disease.  At  least,  it  is  easier 
to  maintain  the  normal  action  than  to  restore  it  when 
impaired. 

217.  Influence   of  Hygiene   on    the   Duration   of 
Life.  —  The  influence  of  a  knowledge  of  hygienic  laws, 
were  that  knowledge  generally  diffused,  would  greatly 
increase  the  average  duration  of  human  life.     It  would 
also  add  very  much  to  the  efficiency  and  value  of  life, 
both  to  the  individual  and  to  the  community,  by  the 
maintenance  of  uniform   good  health,   protracting   the 
vigor  and  efficiency  of  manhood  to  what  we  now  call 
extreme  old  age. 

Of  the  average  life  of  man,  deducting  infancy,  sick- 
ness, and  old  age,  scarcely  more  than  half  is  available 
for  the  purposes  of  active  life.  Nor  should  we  be  sur- 
prised that  men  and  women  are  so  frequently  sick,  and 
so  often  unfit  for  the  duties  or  even  the  enjoyments  of 
life.  When  we  observe  the  almost  constant  violations  of 
the  laws  of  health,  so  common  in  every  community,  we 
wonder  that  people  live  at  all ;  we  are  surprised  at  the 
leniency  and  long-sufFering  of  Nature,  in  so  slowly  and 
tenderly  exacting  the  penalty  of  her  violated  laws. 

218.  Hygiene  in  relation  to  the  Cure  of  Disease.  — 

But  the  rules,  by  the  observance  of  which  health  is 
maintained,  have  an  important  bearing  on  the  cure 
of  disease;  and  it  is  in  this  relation  that  hygiene 
becomes  almost  as  important  to  the  physician  as  to 
the  patient.  The  persistent  violation  of  a  sanitary 
law  finally  wears  out  the  powers  of  resistance  inherent 


154  HYGIENE. 

in  the  vital  force,  and  disease  follows.  No  sensible 
physician  would  even  hope  for  a  cure  of  that  disease 
without  first  restoring  an  enforcement  of  the  violated 
laws :  these  being  restored  and  carefully  observed,  health 
will  generally  follow  with  but  little  aid  from  medicine. 
The  most  perceptible  change  in  the  practice  of  medi- 
cine, within  the  last  fifty  years,  is  the  diminished  con- 
fidence of  enlightened  physicians  in  mere  medication, 
and  their  increased  confidence  in  sanitary  and  hygienic 
measures  for  the  cure  of  disease. 

Recapitulation. 

Hygiene  is  the  art  of  preserving  health.  Disease  is  deranged 
physiological  action.  To  restore  health  is  a  complex  and  diffi- 
cult work,  but  to  maintain  health  is  comparatively  simple  and 
easy.  Vital  force  is  in  the  ratio  of  the  chemical  changes  taking 
place  in  the  body.  This  chemical  action  may  be  too  rapid,  too 
slow,  or  it  may  be  perverted.  Duration  and  value  of  life  de- 
pendent on  the  maintenance  of  health.  Disease  arising  from 
violations  of  the  laws  of  health  is  incurable  while  these  vio- 
lations continue. 


LESSON    XXVII. 

FOOD   AND    DRINK. 

219.  Division  of  the  Subject  —  purposes  of  Food.— 

In  investigating  the  subject  of  hygiene,  we  find  it 
convenient  to  follow  the  same  division  which  we 
adopted  in  the  first  part  of  the  work.  We  will  there- 
fore begin  with  the  hygiene  of  the  Nutritive  system. 


FOOD  AND  DRINK.  155 

This  will  embrace  the  subjects  of  Digestion,  Circulation, 
Respiration,  and  the  Transformation  of  the  tissues. 

The  subject  of  digestion  includes  food  and  drink,  with 
regard,  1st,  to  quality  and  quantity ;  2d,  to  the  time  and 
manner  of  taking  them ;  and,  3d,  to  the  condition  of  the 
system.  As  it  is  the  purpose  of  food  to  supply  mate- 
rial to  repair  the  wastes  of  the  system  from  the  wear  of 
it?  incessant  activities,  it  is  evident  that  it  must  contain 
the  elementary  substances  out  of  which  the  tissues  of 
the  body  are  formed ;  for  the  vital  and  chemical  forces, 
however  strangely  they  may  change  and  modify  the 
forms  of  matter,  can  create  nothing.  Therefore  our 
food  must  furnish  the  material  for  growth  and  repair. 

220.  Organic  and  Inorganic  Substances.  —  In  gen- 
eral terms,  we  may  assume  that  all  digestible  food  is 
derived  from  the  organized  forms  of  matter,  vegetable 
or  animal.  It  is  true  that  a  number  of  substances, 
such  as  water,  common  salt,  lime,  etc.,  enter  into  both 
the  fluids  and  solids  of  the  body;  but  these  undergo 
no  change  by  digestion.  They  enter  the  circulation  by 
absorption,  maintaining  their  true  forms,  and  are  never 
vitalized  in  the  same  manner  that  muscles,  nerves,  and 
membranes  are.  Yet  we  must  not  suppose  that  these 
are  therefore  unimportant  in  the  animal  economy. 

The  inorganic  elements  of  the  body  are,  indeed,  indis- 
pensable for  its  growth  and  health.  Of  these,  water  is 
by  far  the  most  abundant,  and,  we  may  safely  say,  of 
the  most  immediate  importance.  It  is  the  solvent  of 
all  that  goes  into  or  is  carried  out  of  the  system.  It  is 
present  in  all  the  tissues,  and  permeates  even  the 
firmest  solids,  carrying  nutrition  to  them,  and  bearing 
from  them  the  waste  material. 


156  HYGIENE. 

221.  Sources  of  Impurity  in  Water.— Water,  to  be 

fitted  for  the  purposes  of  the  body,  should  be  as  nearly 
pure  as  possible ;  but  absolutely  pure  water  can  be  ob- 
tained only  by  distillation.  Rain-water,  in  falling 
through  the  air,  absorbs  carbonic  acid,  ammonia,  and 
other  gases,  which  are  mixed  in  minute  quantities 
with  the  air;  afterward,  in  percolating  through  the 
earth,  it  dissolves  variable  amounts  of  lime  and  other 
mineral  substances  which  are  found  in  solution  in  the 
water  of  our  springs  and  wells. 

But,  fortunately,  the  gases  from  the  air  or  the  min- 
erals from  the  earth  are  not  often  in  such  quantities 
as  to  greatly  impair  .  the  healthfulness  of  water  as  a 
diet  drink.  Much  has  been  said  of  the  unhealthfulness 
of  what  is  called  hard  ivater,  but  a  comparison  of  lime- 
stone and  freestone  districts  shows  much  less  difference 
in  the  health  of  the  people  living  in  them,  than  we 
might  expect. 

222.  Lime,  how  held  in  Solution  —  Rain-water. — 

Water  holds  lime  in  solution  chiefly  by  aid  of  the 
carbonic  acid  dissolved  in  it ;  but  on  raising  the  tem- 
perature of  the  water,  the  carbonic  acid  escapes  as  a 
gas,  and  the  lime  is  consequently  precipitated.  It  is 
probably  from  this  cause  that  limestone  water  is  com- 
paratively harmless.  As  soon  as  it  enters  the  stomach, 
the  temperature  rises  till  it  reaches  blood-heat,  the 
carbonic  acid  escapes,  and  the  lime  is  precipitated, 
and,  being  indigestible,  is  carried  off  by  the  intes- 
tines. 

Iron  is  frequently  found  in  spring  and  well  waters, 
but  it  is  seldom  in  such  quantity  as  to  materially 
affect  its  healthfulness ;  and  when  such  is  the  case, 


FOOD   AND  DRINK.  1*57 

it  imparts  to  the  water  an  offensive  taste,  which  will 
commonly  prevent  its  use  for  drinking  purposes. 
Rain-water,  well  filtered  through  alternate  layers  of 
coarsely  pulverized  charcoal  and  clean  silicious  sand, 
furnishes  a  diet  drink  sufficiently  pure  for  all  practical 
uses. 

223.  Organic  Impurities  in  Water.  —  But  organic 
impurities,  derived  from  decomposing  animal  and  veg- 
etable matter,  are  much  more  injurious  than  the  ordi- 
nary mineral  impurities  in  water.  Unfiltered  rain- 
water, especially  if  it  has  been  collected  from  a  wooden 
roof,  is  generally  unfit  for  drinking  or  culinary  pur- 
poses; and  river  water  is  seldom  so  free  from  organic 
substances,  in  solution,  as  to  render  it  fit  for  table  or 
kitchen  use. 

Rivers,  springs,  and  shallow  wells  often  become  im- 
pure from  sewage  which  is  mixed  with  them  in  the 
vicinity  of  large  cities.  Sickness  is  sometimes  induced 
by  the  use  of  such  water,  when  neither  the  taste  nor 
smell  of  it  betrays  the  presence  of  the  impurities.  It 
is  hardly  necessary  to  add  that  surface  water,  though 
derived  from  recent  rains,  and  drawn  from  the  surface 
of  clean  meadows  or  woodlands,  is  unfit  for  use  until  it 
has  been  very  thoroughly  filtered. 

224:.  Propej*  Temperature  of  Drinks.  —  For  drinking 
purposes,  W^er  should  have  a  temperature  ranging 
between  fifty-five  and  sixty  degrees  Fahrenheit.  A 
temperature  above  sixty  is  not  palatable,  and  a  lower 
temperature  than  fifty-five  degrees  is  injurious  to  the 
stomach,  and  often  dangerous.  Especially  is  this  true 
of  ice-water  used  at  meals.  Food  requires  a  temperature 
varying  but  a  few  degrees  from  blood-heat  (ninety- 


158  HYGIENE. 

eight),  to  insure  its  rapid  and  perfect  digestion;  but 
if  the  drink  used  at  meals  be  either  ice-cold  or  boiling 
hot,  digestion  will  be  suspended  until  the  contents 
of  the  stomach  has  acquired  nearly  the  natural  tem- 
peratiire  of  the  body. 

Both  ice-water  and  hot  drinks  at  meals  are  un- 
healthy, but  of  the  two,  the  former  is  the  most  inju- 
rious. In  warm  weather,  when  heated  from  exercise, 
ice-cold  water  should  never  be  used,  and  even  water 
at  the  proper  temperature  should  be  taken  slowly 
and  with  caution. 

£25.  Tea,  Coffee,  and  Chocolate.— The  diet  drinks, 
tea,  coffee,  and  chocolate  appear  to  have  been  mis- 
understood until  very  recently.  They  have  generally 
been  classed  with  stimulants  and  narcotics,  but  care- 
ful experiments  have  established  the  fact  that  their 
action  is  to  hasten  the  transformation  of  the  tissues, 
as  is  indicated  by  the  increased  volume  of  carbonic 
acid  exhaled  from  the  lungs  in  a  given  time,  when 
under  their  influence.  The  active  principle  in  each 
of  these  belongs  to  that  family  of  vegetable  alkaloids 
of  which  quinine  is  the  representative. 

But  it  is  not  to  be  inferred  from  this  that  every 
indulgence  in  these  beverages  is  harmless.  Tea  and 
coffee,  besides  the  active  principle,  contain  a  large 
amount  of  astringent  matter  (tannic  aci^/);  which  acts 
unfavorably  on  the  mucous  membrane  of  the  stomach 
and  intestines.  This  is,  however,  modified  to  a  great 
extent  by  the  action  of  milk,  which  should  always  be 
used  with  these  beverages. 

226.  Fermented  Drinks — their  effects.  —  Beer,  ale, 
wine,  and  other  diet  drinks  produced  by  fermentation. 


FOOD  AND  DKINK.  159 

and  consequently  containing  alcohol,  should  be  uncon- 
ditionally rejected  by  every  one  who  wishes  to  main- 
tain good  health.  It  is  the  characteristic  action  of 
alcohol  to  prevent  or  arrest  chemical  change  in  organic 
substances.  But  digestion  is  chemical  change,  and  so 
long  as  the  alcoholic  mixture  is  mingled  with  the  food, 
that  change  is  suspended. 

The  absorbents  of  the  stomach,  however,  soon  remove 
it  into  the  circulation,  but  the  effect  of  its  specific 
action  on  the  nerves  of  the  stomach  remains,  diminish- 
ing and  perverting  the  sensibility  of  that  organ,  so  that 
the  food  in  a  half-digested  state  is  hurried  into  the  in- 
testines, and  the  nutriment  is  lost,  if  nothing  worse 
occurs.  The  glass  of  wine  at  dinner  is  merely  a  bribe 
to  deaden  the  sensibility  of  the  stomach,  overloaded  by 
gluttonous  indulgence,  so  that  it  may  not  complain. 

Recapitulation. 

The  subject  of  digestion,  as  it  relates  to  food,  embraces  quan- 
tity, quality,  time  and  manner  of  taking,  and  the  condition  of 
the  system  when  food  is  taken.  Inorganic  substances  undergo 
no  change  by  digestion.  Impurities  in  water,  and  the  sources 
from  which  they  are  derived.  Mode  of  purifying  rain-water. 
Extremes  of  temperature  in  drinks — their  effect  on  digestion. 
Tea,  coffee,  and  chocolate — their  true  character.  Fermented 
drinks  are  always  injurious. 
B.  P  i4. 


160  HYGIENE. 

LESSON    XXVIII. 

CLASSIFICATION   OF    FOOD. 

227.  Animal  and  Vegetable  Food—  their  essential 
identity.  —  The  classification  of  food  into  animal  and 
vegetable,  which  appears  so  obvious  and  which,  a  few 
years  ago,  was  so  generally  admitted,  is  found,  on  care- 
ful examination,  to  be  without  any  real  foundation. 
Animal  substances  are  all  derived  from  the  vegetable 
kingdom,  and  most  of  the  proximate  principles  entering 
into  the  composition  of  animal  bodies  are  found  already 
formed  in  vegetable  organisms.  The  prejudice  against 
animal  food  is  therefore  without  foundation,  so  far  as 
the  chemical  constituents  of  the  food  is  concerned. 

Animal  food  is  only  a  more  concentrated  state  and 
differently  organized  form  of  the  same  substances  we  find 
in  vegetables.  The  vegetable  world,  however,  contains 
many  proximate  elements  that  are  not  transferred  to 
the  animal  kingdom.  No  one  Substance,  whether  pro- 
duced in  the  vegetable  or  animal  kingdom,  contains  all 
the  material  of  healthful,  nutritious  food;  nor  do  all 
persons  require  the  same  proportions  of  the  various. 
kinds  of  food,  nor  does  the  same  person  under  different 
circumstances. 


228.  The  Three   Groups  of  Food.  —   i      may  be 

conveniently  divided  into  three  groups,  according  to 
their  resemblances  in  composition,  and  the  general 
purpose  which  they  subserve  in  the  animal  economy. 
These  are,  1st.  The  Proteine  or  flesh-forming  group; 
2d.  The  Amylaceous  or  starchy  group;  3d.  The  Ole- 
aginous or  fatty  group. 


CLASSIFICATION  OF  FOOD.  161 

In  their  office  as  food,  the  second  and  third  group, 
though  not  identical,  are  nearly  allied  to  each  other. 
The  old  division  of  food  into  the  carbonaceous  or  heat- 
producing  substances,  and  the  nutritious  or  flesh-form- 
ing materials,  is  found  to  be  faulty,  inasmuch  as  the 
latter,  in  its  chemical  changes,  also  gives  off  heat,  and 
the  changes  in  both  are  connected  with  the  evolution 
of  vital  force. 

229.  The  Proteine  Group — its  several  substances.— 

The  proteine  group  consists  chiefly  of  gluten,  fibrinc, 
albumen,  and  caseine.  These  all  contain  nitrogen,  and 
closely  resemble  each  other  in  their  chemical  compo- 
sition, though  they  differ  materially  in  the  form  of 
their  organization  and  in  their  general  appearance. 
They  decompose  by  putrefaction,  and  give  off  in  that 
process  the  disagreeable  odor  familiarly  known  as  ac- 
companying that  kind  of  decay. 

Gluten  is  found  in  various  kinds  of  grain,  in  fruits, 
and  in  numerous  vegetables,  such  as  asparagus,  cab- 
bages, etc.  It  is  easily  Obtained  by  washing  the  starch 
from  flour  with  cold  water.  It  is  a  tough,  elastic  sub- 
stance, of  a  light  gray  color,  without  odor,  and  with  a 
slightly  sweetish  taste.  Its  composition  is  the  same  as 
that  found  in  the  lean  flesh  of  animals,  the  two  differing 
only  in  the  manner  in  which  they  are  organized. 

230,  Fibrine,  Albumen,  and  Caseine.  —  Fibrine  is 
found  in  solution  in  the  blood  of  animals,  and  is  pre- 
cipitated when  the  blood  is  cooled,  forming  the  essential 
part   of  the  coagulum,  or  clot,  from  which  it  may  be 
obtained   by  washing  with  cold  water.     It  is  the  sub- 
stance  from   which   most  of  the   fibrous  tissues  of  all 
animals  are  formed. 


162  HYGIENE. 

Caseine  is  the  curd  or  solid  part  of  milk,  which  is 
separated  by  coagulation,  and  therefore  forms  the  chief 
ingredient  in  cheese,  as  it  is  the  chief  element  of  nutri- 
tion in  milk.  It  is  found  in  the  seeds  of  many  plants, 
such  as  peas,  beans,  etc.  Albumen  is  found  nearly 
pure  in  the  white  of  eggs.  It  dissolves,  to  a  limited 
extent,  in  cold  water,  but  coagulates  and  hardens  in 
water  a  little  below  the  boiling  temperature.  It  occurs 
in  nearly  all  the  fluids  of  the  living  body,  and  forms  a 
large  proportion  of  the  brain.  It  has  also  been  detected 
in  the  seeds  of  many  vegetables. 

231.  Gelatine — its  properties  and  use.  —  Gelatine,  a 
substance  often  associated  with  this  group,  differs  essen- 
tially from  those  just  described,  both  in  chemical  com- 
position and  in  material  form.     The  animal  matter  in 
bones,  the  substance  of  tendons,  ligaments,  etc.,  is  gela- 
tine.    Glue  is  the  form  in  which  it  is  most  familiar. 
While  the  true  proteine  compounds  are  convertible  into 
one  another  in  the  animal  economy,  gelatine  can  not  be 
appropriated   to   any   purpose    but   the   formation   and 
repair  of  bone,   tendon,   ligament,   etc. 

It  is  sparingly  soluble  in  cold  water,  but  dissolves 
readily  in  that  fluid  at  or  near  the  boiling  point.  It  is 
the  essential  ingredient  in  soups  and  animal  jellies. 
The  fact  that  it  can  not  be  appropriated  to  the  repair 
or  growth  of  the  soft  tissues  of  the  body,  corrects  a 
popular  mistake  in  regard  to  the  very  nutritious 
quality  of  soup. 

232.  The  Tissues  — whence  derived.  — All  the  tis- 
sues of  the  body  are  derived  from  the  proteine  group 
of    alimentary   substances    and    from    gelatine;    conse- 
quently their   growth   and   constant   repair  depend  on 


CLASSIFICATION  OF   FOOD.  163 

a  sufficient  supply  of  these,  in  such  form  and  condi- 
tion as  will  enable  the  stomach  most  readily  to  digest 
them,  and  place  them  in  favorable  circumstances  to  be 
assimilated.  It  is  of  but  little  consequence  whether 
they  are  derived  from  their  original  forms  in  the  vege- 
table world,  or  fcom  the  secondary  forms  of  animal  or- 
ganization, but  it  is  of  the  first  importance  that  these 
be  in  a  sound  condition,  entirely  free  from  any  taint 
of  decomposition  or  putrefaction. 

Animal  food  is  usually  preserved  from  decay  by  an 
excess  of  salt  (chloride  of  sodium),  which  requires  to  be 
dissolved  out  by  the  fluids  of  the  stomach  before  diges- 
tion takes  place.  Salt  meats  are  therefore  not  so  readily 
digested  as  fresh. 

233.  The    Amylaceous    Group  —  its    office.  —  The 

second  group  of  alimentary  substances  comprises  starch 
and  the  several  forms  of  sugar,  gums,  etc.  From  this 
group  is  derived  by  far  the  largest  bulk  of  our  food; 
and  in  whatever  form  it  comes  to  us,  it  is  the  product 
of  vegetable  life.  All  the  members  of  this  group  con- 
tain the  same  chemical  elements,  and  differ  only  in  the 
proportions  in  which  these  are  combined.  They  are 
especially  rich  in  the  two  combustible  substances,  car- 
bon and  hydrogen.  This  fact  indicates  the  office  of  the 
starch  and  sugar,  which,  in  the  form  of  bread,  potatoes, 
fruits,  and  other  vegetable  productions,  enter  so  largely 
into  our  daily  bill  of  fare. 

In  combining  with  the  oxygen  inhaled  by  the  lungs, 
these  undergo  a  true  combustion.  From  this  source, 
and  from  the  oxidation  of  the  waste  matter  of  the 
tissues,  are  derived  the  animal  heat  and  working  force 
expended  by  the  body. 


164  HYGIENE. 

2M.  The  Oleaginous  Group— the  use  of  Oils  and 
Fats.  —  The  oleaginous  group  consists  of  various  oils 
and  fats,  derived  both  from  the  vegetable  and  the 
animal  world.  Like  the  members  of  the  other  groups, 
they  are  closely  allied  to  each  other  in  composition, 
and  are  convertible  each  into  the  other  in  the  vital 
economy.  The  oils  are  non-nitrogenized  bodies,  made 
of  the  same  elementary  substances  as  those  composing 
tho  second  group,  but  containing  much  less  oxygen. 
They  therefore  form  the  highest  grade  of  heat-producing 
food,  and  are  in  demand  in  cold  temperatures  and 
with  those  exposed  to  the  winter  climate  of  the  tem- 
perate zones.  Fatty  matter  is  also  found  in  the  brain, 
and  is  probably  an  essential  constituent  of  that  impor- 
tant organ. 

Recapitulation. 

Animal  and  vegetable  forms  of  food  contain  the  same  proxi- 
mate elements.  Food  is  divided  into  three  groups  —  the  pro- 
teine,  the  amylaceous,  and  the  oleaginous.  The  tissues  are 
derived  from  the  proteine  forms  of  food.  The  proteine  ele- 
ments are  formed  in  vegetables  and  transferred  to  animals. 
The  amylaceous  group  supplies  the  largest  portion  of  our  daily 
food.  Both  the  amylaceous  and  the  oleaginous  groups  furnish 
heat-producing  food.  They  consist  chiefly  of  combustible  ele- 
ments. 


QUALITY  OF  FOOD.  165 


LESSON    XXIX. 

QUALITY   OF    FOOD. 

235.  Yolume  of  Food  important.  —  Before  we  pro- 
ceed to  name  the  several  articles  of  food  which  go  to 
make  up  our  bill  of  fare,  it  may  be  well  to  say  that  the 
value  of  any  particular  article  does  not  depend  alto- 
gether on  the  amount  of  nutritious  matter  it  contains. 
Nutriment  may  be  so  concentrated  or  so  combined  as  to 
render  its  digestion  difficult,  if  not  impossible. 

The  stomach  requires  a  certain  degree  of  distention 
for  the  ready  and  perfect  performance  of  its  function. 
To  secure  this  distention,  volume  or  bulk  in  the  food 
is  required,  at  least  to  a  certain  extent.  An  ounce 
of  concentrated  nutriment  mixed  with  half  a  pound 
of  inert,  indigestible  matter,  will  generally  be  digested 
much  more  readily  than  if  it  were  taken  unmixed. 
The  nutritious  elements  of  food  may  be  so  combined 
as  to  render  their  separation  difficult,  and  consequently 
their  digestion  slow  and  imperfect. 

230.  Milk  as  a  perfect  Diet.  —  Milk  comes  nearer 
supplying  all  the  demands  of  a  complete  nutrition  than 
any  other  substance.  It  has,  therefore,  been  generally 
regarded  as  the  perfect  type  of  food,  and  other  articles 
have  been  measured  by  this  standard.  This,  however, 
is  true  only  of  young  or  growing  persons;  but  in  adults 
engaged  in  active  and  laborious  employments,  it  fails 
to  furnish  a  necessary  proportion  of  combustible  or 
heat  and  force-producing  elements. 

Milk  from  different  animals  varies  considerably  in  its 
composition,  and  even  from  the  same  animal,  under 


166  HYGIENE. 

different  circumstances  of  food,  exercise,  temperature, 
etc.,  a  considerable  variation  in  quality  is  observed. 
The  average  of  a  number  of  specimens  of  milk,  taken 
from  several  cows,  gives,  in  a  hundred  parts,  4.48 
parts  of  caseine  or  cheesy  matter,  3.13  of  butter,  4.47 
of  sugar  of  milk,  .60  of  saline  matter,  and  87.32  of 
water. 

237.  Milk,  by  what  circumstances  modified.  —  In 

most  stomachs,  milk  is  more  digestible  when  quite 
fresh,  but  there  are  conditions  of  that  organ  in  which 
the  lactic  acid,  formed  when  milk  coagulates,  is  re- 
quired to  supplement  the  deficiency  of  acid  in  the 
gastric  fluid.  This  relates,  however,  to  a  morbid  and 
not  to  a  normal  condition  of  the  digestive  organs.  Milk, 
when  used  as  a  diet  drink,  should  have  a  temperature 
not  lower  than  sixty  degrees. 

Iced  milk,  taken  at  meals,  suspends  the  digestion  of 
the  food  till  the  whole  mass  has  acquired  the  natural 
temperature  of  the  body;  and  sometimes  this  interrup- 
tion so  disturbs  the  whole  process,  that  the  work  is  very 
imperfectly  done.  Milk  is  much  affected  by  the  food 
of  the  cow  producing  it,  and  certain  odors,  such  as 
clover-bloom  and  others  less  agreeable,  can  readily  be 
detected  in  the  milk  when  fresh.  From  this  cause, 
decaying  or  putrescent  food  and  slops  should  never  be 
fed  to  cows  giving  milk. 

238.  Cheese  and  Butter  —  their  dietetic  value. — 

Cheese  is  a  product  from  milk,  and  contains,  when 
properly  made,  the  caseine  and  most  of  the  butter, 
together  with  a  considerable  proportion  of  the  milk 
sugar.  It  is  a  highly  concentrated  form  of  food,  and 
therefore  it  should  never  be  eaten  alone,  but  always 


QUALITY   OF  FOOD.  167 

with  the  more  crude  and  bulky  forms  of  vegetable 
diet.  Mixed  in  this  manner,  cheese  digests  readily, 
and  furnishes  a  large  amount  of  material  for  repairs 
in  active  bodies.  Taken  by  itself,  it  is  hard  of  diges- 
tion, and  often  produces  serious  disturbances  of  the 
stomach. 

Butter  is  a  true  fat,  but  more  complex  in  its  char- 
acter than  the  other  oils,  whether  animal  or  vegetable; 
and  from  this  cause  it  is  more  liable  to  chemical 
changes,  producing  certain  acids  which  give  the  rancid 
character  to  it,  and  greatly  impair  its  dietetic  value. 
It  is  purely  a  heat  and  force-producing  article,  and 
furnishes  nothing  to  growth  or  repair. 

239.  Eggs  very  nutritious  —  how  to  cook  them.— 

Eggs  consist  chiefly  of  albumen  and  the  mineral  salts, 
especially  those  whose  acids  are  derived  from  phos- 
phorus and  sulphur.  They-  are,  therefore,  a  very  per- 
fect but  a  very  concentrated  form  of  food.  However, 
albumen  is  the  most  digestible  form  of  all  the  proteine 
group,  and  eggs,  if  properly  prepared,  seldom  fail  to  be 
digested,  though  taken  alone. 

Mixed  with  a  proper  measure  of  food  containing 
starch,  so  as  to  increase  the  bulk  and  furnish  an 
additional  supply  of  the  heat-producing  material,  there 
is  no  more  nutritious  and  healthful  diet  than  fresh 
eggs.  Those  of  barn-yard  fowls  are  always  to  be  pre- 
ferred to  the  eggs  of  water  fowls.  Eggs,  though  very 
nutritious  in  themselves,  are  often  so  injured  in  cook- 
ing as  to  render  them  almost  indigestible.  By  what- 
ever method  they  are  cooked  (and  boiling  is  the  best), 
the  white  should  be  merely  coagulated  and  the  yolk 
left  soft. 

B.  P.— 15. 


168  HYGIENE. 

240.  Animal  Flesh  —  kinds   and   value.  —  Animal 
flesh  furnishes   a   concentrated   and   highly  nutritious 
food.     In   most  of   its  forms   it   is  easily  digested  and 
readily   assimilated.     There    is   quite   a    wide    margin, 
however,  between   different    kinds   of  meat,  in  regard 
to   the    amount  of  available    nutrition,  as   well   as   to 
the   ease   with  which  they  are  digested  and  incorporated 
into  the  living  tissues. 

Beef,  pork,  and  mutton  are  the  most  common  forms 
in  which  animal  flesh  is  met  with  on  American  tables. 
Of  these,  mutton  is  the  most  digestible,  but  beef  con- 
tains the  highest  per  cent  of  nutriment.  Pork  is  of 
value  chiefly  for  the  large  amount  of  oil  it  furnishes, 
and  its  consequent  high,  heat-producing  quality.  It 
is  therefore  well  adapted  to  use  in  cold  climates  and 
in  the  winter  season.  The  animal  fats  should  be  used 
with  caution  and  sparingly  in  warm  weather,  but  never 
in  hot  climates. 

241.  Necessary  Precaution  in  Fattening  Animals 
for  Food.  —  The  flesh  of  young  animals  is  more  easily 
digested  than  that  of  the  more  mature.     An  important 
exception  to  this  rule  may  be  mentioned :  beef  is  more 
digestible  than  veal.    The  good  quality  of  meat  depends 
much  on  the  manner  in  which  it  is  fed  and  prepared 
for   the   market.     The  best  beef   is   fattened   on   fresh 
pastures,  with  but  little  grain.     This  mode  of  fattening 
tends  to  develop  the  muscular  or  fleshy  part  of  the  ani- 
mal, and  diffuse  the  fat  through  the  flesh,  rather  than  to 
accumulate  it  in  masses,  as  is  done  in  stall-feeding. 

Animals  fattened  on  the  slops  of  distilleries  and  the 
wastes  of  breweries  are  entirely  unfit  for  food,  and 
should  not  be  offered  in  the  markets.  Animals  taken 


QUALITY  OF  FOOD.  169 

to  market  by  long  journeys,  whether  on  foot  or  in 
crowded  cars,  are  not  suitable  for  food  till  they  have 
fully  recovered  from  the  journey. 

242.  Wholesome  Meat— how  distinguished.  —  The 

flesh  of  good  beef,  pork,  or  mutton  should  be  a  light 
red,  approaching  toward  the  scarlet  hue.  A  pale  color 
indicates  an  immature  animal,  and  dark  red  meat 
shows  an  animal  too  old  and  tough  to  be  savory,  or 
that  it  had  been  suffering  from  the  effects  of  a  long 
journey  to  market. 

Wholesome  meat  should  be  entirely  free  from  even 
a  tendency  to  putrefaction.  This  can  not  always  be 
detected  by  the  odor,  for  meat  kept  on  charcoal  or  on 
ice  will  frequently  be  far  advanced  in  the  first  stages 
of  decomposition,  and  yet  emit  no  unpleasant  gases. 
If,  on  cutting  the  flesh,  the  surface  appears  mottled, 
or  marbled  with  pale  spots,  and  if  the  fibers  be  easily 
torn  across,  it  will  be  safe  to  reject  such  meat.  The 
fat  of  pork  and  mutton  should  be  white  and  firm,  even 
in  warm  weather,  and  that  of  beef  but  slightly  tinged 
with  yellow. 

Recapitulation. 

Concentrated  food  is  difficult  of  digestion.  Milk  is  a  perfect 
food  only  for  growing  persons.  The  com  position,  of  milk.  It 
varies  with  the  circumstances  of  the  animal  from  which  it  is 
derived.  Cheese  is  a  very  concentrated  form  of  food,  and 
therefore  should  never  be  taken  alone.  Butter  belongs  to  the 
oleaginous  group.  Eggs  form  a  very  nutritious  diet,  and  when 
properly  cooked,  are  easily  digested.  Animal  flesh— difference 
in  the  several  kinds.  The  kind  of  food  on  which  animals  are 
fattened  affects  the  quality  of  their  flesh. 


170  HYGIENE. 


LESSON    XXX. 

QUALITY   OF    FOOD  — CONTINUED. 

243.  Flour— its  composition— different  varieties. — 

The  amylaceous  or  starchy  group  is  represented  chiefly 
by  the  cereal  grains,  such  as  wheat,  rye,  Indian  corn, 
barley,  etc.  Of  these,  wheat  is  the  most  important, 
as  it  approaches  nearer  to  a  perfect  diet  than  any 
other  product  of  the  vegetable  world.  Different  samples 
of  wheat  vary  somewhat  in  the  proportions  of  the  dif- 
ferent proximate  elements  entering  into  its  compo- 
sition. 

This  arises  from  the  many  varieties  of  wheat  cul- 
tivated, and  from  the  quality  of  the  soil  on  which  it 
is  grown.  The  average  may  be  stated  at  twelve  per 
cent  of  gluten,  seventy  per  cent  of  starch,  and  ten 
per  cent  of  water;  the  remaining  eight  per  cent  consists 
of  sugar,  oil,  and  phosphates  of  lime,  potash,  and  mag- 
nesia. These  proportions  are  seldom  found,  however, 
in  fine  flour.  The  central  portion  of  the  grain  consists 
almost  entirely  of  starch,  while  the  outer  part,  near 
the  cuticle  or  bran,  is  rich  in  gluten  and  the  mineral 
salts.  In  the  common  methods  of  manufacturing  flour, 
these  are  chiefly  lost,  by  not  being  made  fine  enough 
to  pass  through  the  bolting  cloth. 

244.  Adulteration  and  Deterioration  of  Flour.  - 

From  this  cause,  very  fine  flour  is  less  nutritious 
than  that  of  a  coarser  grade.  Brown  bread,  made  of 
unbolted  flour  ground  closely,  contains  all  the  nutri- 
ment of  the  grain  in  a  very  digestible  form;  and  for 
persons  of  feeble  digestive  powers,  it  is  always  to  be 


QUALITY  OF  FOOD.  171 

preferred  to  fine  bread.  Flour  is  sometimes  adulterated 
by  mixtures  of  carbonate  of  lime  or  chalk.  This  can 
be  detected  by  a  grittiness  in  chewing  the  flour  or 
the  bread  made  from  it. 

Adulterations  from  mixture  of  cheaper  grains  are 
difficult  to  detect,  but,  fortunately,  they  are  of  less 
consequence,  as  they  but  slightly  diminish  the  nutri- 
tive value  of  the  food.  Flour  becomes  whiter  by  age, 
but  this  improved  appearance  is  at  the  expense  of  its 
sweetness  and  real  value.  The  richer  flour  is  in  gluten, 
the  more  rapidly  it  deteriorates. 

245.  Rye    and    Corn    as    Bread    Materials.  —  Rye 

furnishes  a  wholesome  bread,  though  it  is  much  darker 
than  that  made  from  wheaten  flour.  It  contains  more 
sugar  and  oil  than  wheat,  has  a  heavier  bran  and  a 
smaller  proportion  of  starch.  In  the  gluten,  the  nitro- 
genized  matter  resembles  caseine  from  milk,  while  that 
from  wheat  flour  more  nearly  resembles  fibrine.  In  del- 
icate stomachs  it  is  not  easily  digested;  and  it  is  much 
more  difficult  to  make  good  bread  from  rye  than  from 
wheat  flour. 

Indian  corn  contains  a  larger  proportion  of  oil  than 
any  other  grain  known.  This,  howrever,  differs  very 
materially  in  the  different  varieties  of  corn.  Those 
known  as  flint  corn  yield  more  than  double  as  much 
oil  as  the  varieties  with  large,  spongy  grains.  The 
quantity  of  sugar,  also,  is  far  from  being  constant. 
It  is  very  rich  in  starch,  but  in  the  nitrogenized  or 
flesh-producing  element,  it  is  poorer  than  any  bread 
material  in  use,  excepting,  perhaps,  buckwheat.  This 
is  not  in  the  form  of  gluten,  as  found  in  other  grains, 
but  in  a  peculiar  form  called  zcine. 


<l 


172  HYGIENE. 

246.  Preparation  of  Corn  for  Food.  —  From  these 
peculiarities  it  lacks  the   adhesive   qualities   of  dough 
from    wheat   or   rye    flour,   and    therefore   the   bread   is 
made   light   by   fermentation,  with  difficulty.     In    pre- 
paring  articles   from   corn   meal,   a  longer   time   is   re- 
quired to  cook  them  thoroughly  than  is  necessary  when 
other   bread   materials    are    used.     But   when    properly 
cooked,  corn  meal  furnishes  a  palatable,  highly  nutri- 
tious, and  easily  digested  food. 

Barley  and  oats  are  but  little  used  as  bread  material 
in  this  country,  though  in  some  parts  of  the  world 
they  form  an  important  part  of  the  daily  food  of  a 
large  population.  They  are  rich  in  sugar  and  gluten, 
but  poor  in  starch  and  the  phosphates,  as  compared 
with  wheat.  Rice  is  seldom  used  for  bread.  It  is  very 
digestible,  consisting  of  nearly  pure  starch,  with  the 
smallest  quantity  of  gluten  and  oil. 

247.  Beans  and  Peas  —  their  dietetic  value.  —  Peas 

and  beans  can  hardly  be  classed  with  this  group,  as 
they  contain  from  twenty-five  to  thirty  per  cent  of 
nitrogenous  matter,  in  the  form  of  vegetable  caseine; 
but  as  there  appears  to  be  no  more  appropriate  place 
for  them,  wre  have  assigned  them  here.  They  are  highly 
nutritious,  but,  like  most  other  concentrated  forms  of 
nutritive  matter,  they  are  hard  to  digest,  and  if  not 
readily  digested,  they  are  apt  to  produce  flatulency  and 
other  derangements  of  the  digestive  apparatus.  Taken 
in  the  unripe  state,  they  are  less  objectionable  in  this 
respect. 

As  a  substitute  for  animal  food,  to  laborers  and  others 
following  active  employments,  there  is  no  form  of  veg- 
etable food  so  well  adapted  as  peas  and  beans.  They 


QUALITY  OF  FOOD.  173 

arc  rich  in  sulphur  and  the  phosphates,  and  contain 
sufficient  starch  to  furnish  heat-producing  material 
even  for  winter  food. 

248.  Potatoes  —  their    composition    and    use    as 
Food.  —  There  is  a  class  of  succulent   vegetables   ex- 
tensively  used  as  food,  which   is   allied   more   qr   less 
remotely  to   this   group   of  starchy  foods.     The   potato 
properly  stands  at  the  head  of  this  list.     Well  matured 
potatoes   contain,   in   one   hundred   parts,  seventy-four 
parts  of  water,  twenty-three   parts  of  starch,   one   and 
one-half   parts   of    gluten,  and   one    part   earthy   salts, 
with  but  a  small  fraction  of  oil.     It  will  be  observed, 
the    proportion    of    flesh-producing    material,   is    very 
small.     They   should,   therefore,    always    be    associated 
with    animal    food   to   supply   this   defect,   as    well    as 
that  of  the  oily  matter. 

Potatoes,  when  properly  cooked,  are  easily  digested; 
and  being  a  bulky  form  of  food,  are  well  adapted  to 
accompany  the  more  concentrated  articles  of  diet,  not 
merely  to  give  distention  to  the  stomach,  but  to  pro- 
mote the  digestion  of  those  highly  nutritious  articles 
that  are  often  difficult  of  digestion. 

249.  Other  Succulent,  Vegetables.  —  Turnips,  beets, 
carrots,  and   parsnips,   constitute   an    important   group 
in   this   class    of   succulent    vegetables.     They  contain 
even    more    water   than    potatoes,   and   the    solid   part 
consists   largely  of   sugar,    instead  of  starch,    and   the 
proportion  of  nitrogenous  elements  is  somewhat  larger 
than  in  the  potato.     They  are  rather  hard  of  digestion, 
and  should  be  used  sparingly  by  persons  whose  habits 
of  life  are  not  very  active,  or  whose  digestive  powers 
are  feeble. 


174  HYGIENE. 

Asparagus,  onions,  and  cabbage  contain  but  little 
starch.  They  are,  however,  well  supplied  with  the 
flesh-forming  elements,  and  are  therefore  very  nutri- 
tious when  properly  prepared.  Onions  contain  an  es- 
sential oil,  on  which  their  peculiar  odor  depends.  This 
oil  is  indigestible,  but  being  volatile,  it  is  absorbed 
from  the  stomach,  and  passing  to  the  lungs,  is  exhaled, 
giving  the  disagreeable  odor  to  the  breath.  Thorough 
boiling  removes  the  greater  portion  of  this,  and  leaves 
a  very  nutritious  food. 

250.  Fruits  —  their  importance  as  diet.  —  Fruits 
consist  mainly  of  water,  with  variable  quantities  of 
starch,  sugar,  and  gum.  Many  kinds  of  fruit  furnish 
a  fair  supply  of  gluten,  and  are  on  that  account  highly 
nutritious.  Their  chief  value,  however,  as  diet,  is  in 
the  various  forms  of  vegetable  acid  which  they  contain, 
in  such  combination  with  the  alkaline  and  earthy  car- 
bonates, as  supply  an  important  want  in  the  process 
of  digestion,  as  well  as  furnish  the  lime  and  potash 
which  they  contain  for  the  use  of  the  .animal  economy. 

Most  of  these  acids  are  laxative,  and  are  therefore 
well  adapted  to  persons  predisposed  to  habits  of  con- 
stipation. This  is  especially  true  of  the  malic  acid, 
which  abounds  in  apples,  peaches,  pears,  etc.  The 
tartaric  acid,  so  abundant  in  grapes  and  berries  gen- 
erally, is  not  only  a  laxative,  but  tends  to  increase  the 
secretion  of  the  skin  and  kidneys. 

Recapitulation. 

The  amylaceous  group  is  represented  chiefly  by  the  cereal 
grains.  Wheat  is  the  most  important  of  these.  Fine  flour  is 
not  so  nutritious  as  coarse.  Flour  deteriorates  by  age.  Rye 
contains  more  sugar  and  oil  than  wheat,  and  a  smaller  propor- 


MODE  OF  PKEPARING  FOOD.  175 

tion  of  starch.  Indian  corn  is  rich  in  oil  and  starch.  Its  nitro- 
genous element  has  a  peculiar  form.  Beans  and  peas  are  very 
nutritious,  but  hard  to  digest.  Potatoes  are  rich  in  starch,  but 
deficient  in  the  proteine  elements.  Asparagus,  onions,  and  cab- 
bage are  lacking  in  starch,  but  abound  in  proteine  elements. 
Fruits  are  important  on  account  of  the  acids  they  furnish  to 
assist  digestion. 


LESSON    XXXI. 

MODE   OF    PREPARING   FOOD. 

251.  Cooking  Food  —  what  is  gained  by  it.  —  The 

natural  quality  of  the  different  articles  of  food  is 
scarcely  less  important  than  is  the  mode  of  preparing 
them  for  the  table.  But  few  articles  of  diet  are  fit  for 
food  without  some  preparation.  This  is  usually  done 
by  the  aid  of  heat.  Cooking,  when  properly  performed, 
accomplishes  two  objects:  1st.  By  rendering  the  sub- 
stances soft,  they  are  easily  masticated,  and  more  read- 
ily dissolved  in  the  gastric  fluid ;  and,  2d.  The  peculiar 
flavor  of  the  food  is  developed,  so  that  it  is  more  agree- 
able to  the  taste. 

This  is  generally  the  result  of  cooking,  though  there 
are  some  very  well  marked  exceptions  to  the  rule. 
For  example,  cabbage  cut  fine,  and  dressed  with  di- 
luted vinegar,  is  more  digestible  than  when  cooked  in 
any  form.  The  flavor  of  some  kinds  of  fruit  is  so 
volatile  that  it  escapes  in  cooking,  and  thus  the  fruit 
is  rendered  insipid.  Long  continued  boiling  produces 
this  effect  on  nearly  all  kinds  of  vegetables. 

252.  Meat — general   rule  for  cooking  it.  —  Meats 
are  prepared  for  the  table  by  several  methods,  such  as 


176  HYGIENE. 

boiling,  roasting,  baking,  broiling,  frying,  etc.  One 
general  rule  applies  to  all  these  methods,  and  its  ob- 
servance is  indispensable  if  we  would  preserve  the 
good  qualities  of  flesh. 

All  wholesome  meats  contain  a  good  proportion  of 
albumen.  This  substance  is  familiar  to  us  in  the  white 
of  eggs.  It  dissolves  readily  in  warm  water,  but  if  the 
temperature  be  raised  to  near  the  boiling  point,  it  is 
instantly  hardened,  and  becomes  entirely  insoluble  in 
water.  To  preserve  this  property  of  meat  is  essential 
alike  to  its  nutritive  quality  and  good  taste.  A  high 
heat  should  therefore  be  applied  to  meat  at  the  begin- 
ning, and  as  the  cooking  proceeds,  the  heat  may  be 
reduced.  This  coagulates  the  albumen  on  the  outside, 
and  thus  prevents  the  escape  of  the  nutritive  juices. 

253.  Boiling  Meat  —  the  Rules.  —  When  meat  is 
cooked  by  boiling,  the  pieces  should  be  large,  and  the 
water  raised  to  the  boiling  point  before  the  meat  is  put 
in.  By  this  means  its  flavor  may  be  preserved  nearly 
perfect,  and  the  loss  in  weight  greatly  diminished. 
This,  in  the  ordinary  method  of  boiling  meat,  amounts 
to  nearly  one-third  of  the  original  weight.  After  boil- 
ing rapidly  for  ten  minutes,  tl\e  heat  should  be  lowered 
to  about  one  hundred  and  seventy  degrees,  or  to  a  point 
below  any  perceptible  boiling,  and  should  be  retained 
at  that  temperature  till  the  fiber  is  fully  softened  and 
tender. 

If  the  object  is  to  make  soup,  the  meat  should  be 
put  into  cold  water,  and  the  temperature  of  about  one 
hundred  and  fifty  degrees  maintained  for  two  or  three 
hours,  when  a  few  minutes  of  rapid  boiling  will  com- 
plete the  process.  Soft  water  is  a  better  solvent  than 


MODE  OF  PKEPAKING  FOOD.  177 

hard,  therefore  soup  should  be  made  with  soft  water, 
and  the  salt  should  not  be  added  till  the  last  stage 
of  the  process.  The  opposite  course  should  be  followed 
when  meat  is  boiled  for  other  purposes. 

254.  Roasting,     Broiling,     Baking,    and     Frying 
Meat.  —  Meat    is   cooked   with   a   direct   application   of 
heat   by    roasting,   broiling,   or  baking.     By   either   of 
these  methods  the  flavor  of  the  meat  is  better  retained 
than  when  cooked  by  boiling,  but  care  must  be  taken 
not   to  overdo  the   cooking,  and  thus   render  the  fiber 
hard,  insipid,  and  indigestible.     The  same  rule  should 
be  observed  in  the  application  of  heat  when   cooking 
meat  by  these  methods  as  by  boiling  (§  253). 

Frying  is  in  all  respects  the  worst  method  of  cooking 
meat.  It  expels  the  natural  fluids  from  the  flesh  fiber, 
and  substitutes  oil  for  these.  When  meat  is  cooked  by 
frying,  the  fat  should  be  heated  very  hot  before  the 
meat  is  put  in,  and  it  should  be  cooked  rapidly,  and 
removed  as  soon  as  it  is  tender. 

255.  Cooking   Vegetables.  —  Vegetables   are   usually 
cooked  by  boiling ;  potatoes,  however,  are  often  prepared 
by  baking ;  and  when  it  is  carefully  done,  the  result  is 
very   satisfactory.     When    vegetables    are    boiled,   care 
must  be  taken  that  the  process  be  not  carried  too  far. 
As  soon  as  the  vegetable  is  soft  it  should  be  removed  at 
once  from   the   boiling  water.     If  the  cooking  be    con- 
tinued beyond  this  point,  the  structure  will  be  broken 
down,  and  much  of  the  vegetable  will  be  dissolved  in 
the  water  and  lost. 

Potatoes,  especially,  should  not  be  suffered  to  remain 
in  the  water  a  moment  after  boiling  has  ceased.  While 
boiling,  the  pores  of  the  vegetable  are  filled  with  steam, 


178  HYGIENE. 

but  as  soon  as  the  temperature  falls  below  the  boiling 
point,  the  steam  begins  to  condense,  and  the  surround- 
ing water  is  drawn  in  to  fill  the  vacuum,  and  the  potato 
is  water-soaked  and  indigestible.  To  a  less  extent,  the 
same  is  true  of  beets,  carrots,  and  parsnips. 

256.  Bread — its  importance  as  a  diet.  —  The  prep- 
aration of  farinaceous  food  in  the  form  of  bread  is  at 
once   the   most  difficult   and   the   most   important   part 
of  the  culinary  art.     In  civilized  countries  bread  is  a 
constant  diet,  a  part  of  every  meal ;   and  if  it  be  badly 
made,  unwholesome,  and  indigestible,  the  mischief  will 
be  in  proportion  to  its  universal  use. 

The  method  of  preparing  bread  by  fermentation  has 
undergone  no  material  change  since  the  days  of  the 
oldest  monuments  of  Egypt;  and  yet  fermentation  is 
not  essential  to  the  production  of  a  wholesome  and 
digestible  bread.  Indeed,  fermentation  is  incipient 
decay,  and  all  substances  are  less  wholesome  and  nutri- 
tious after  decomposition  than  before.  So  we  find 
crackers,  and  kindred  forms  of  unleavened  bread,  more 
digestible  and  nutritious  than  the  ordinary  form  of  fer- 
mented bread.  In  fermentation,  Hour  loses  all  the 
sugar  it  originally  contained,  and  this  loss  amounts 
to  from  six  to  ten  per  cent  of  the  whole  weight. 

257.  Fermenting  Bread  —  rules  to  be  observed.— 

In  making  fermented  bread,  the  chief  secret  lies  in 
producing  a  rapid  action;  and  to  secure  this,  good, 
undamaged  flour  and  fresh,  active  yeast  must  be  used, 
with  a  temperature  of  about  one  hundred  degrees 
steadily  maintained.  If  fermentation  begins  slowly, 
or  if  it  be  arrested  after  it  has  commenced,  either  by 
too  high  or  too  low  a  temperature,  the  first  products 


MODE  OF  PKEPARING  FOOD.  179 

of  fermentation  will  pass  to  the  second  stage,  acetic 
acid  will  be  formed,  and  the  dough  thus  soured  will 
be  spoiled. 

There  is  much  more  danger  of  fermentation  going  too 
far,  and  the  bread  being  sour,  than  there  is  of  arresting 
it  at  too  early  a  stage  by  baking  it.  A  very  palatable 
and  wholesome  bread  is  made  by  forcing  carbonic  acid 
into  the  dough,  under  a  high  pressure,  as  it  is  being 
mixed.  But  this  "aerated  bread"  can  be  produced 
only  by  expensive  machinery,  and  therefore  can  not. 
be  made  in  common  domestic  establishments. 

258.  The    Qualities    of    Wholesome    Bread.  —  By 

whatever  method  bread  is  produced,  rapid  and  thor- 
ough baking  is  indispensable  to  a  palatable  and  digest- 
ible article.  The  bread  should  not  shrink  on  cooling, 
and  there  should  be  no  clamminess  on  cutting  a  loaf. 
Several  kinds  of  "baking  powders"  are  in  use  to  pro- 
duce spongy  bread  without  fermentation.  These  consist 
of  carbonates  of  soda  or  potash,  mixed  with  some  of  the 
vegetable  acids,  or  with  phosphoric  acid.  The  last  is 
the  least  objectionable,  as  the  salt  resulting  from  the 
combination  is  comparatively  harmless. 

Perhaps  the  best  method  to  obtain  carbonic  acid,  to 
lighten  bread  without  fermentation,  is  to  mix  good  bi- 
carbonate of  soda  with  dry  flour,  and  a  weight  of  pure 
muriatic  (chloro  hydric)  acid  equal  to  the  soda,  with 
the  fluid  used  to  moisten  the  mass.  The  gas  will  be  set 
free,  and  nothing  but  common  salt  will  be  formed. 

Recapitulation. 

Cooking  renders  food  more  easily  digested  and  develops  its 
flavor.  Meat  is  cooked  by  boiling,  roasting,  baking,  broiling, 


180  HYGIENE. 

and  frying.  There  is  one  general  rule  for  applying  the  heat, 
to  be  observed  in  all  these  methods.  Danger  of  boiling  veg- 
etables too  long.  They  should  be  removed  from  the  water 
while  it  is  yet  boiling.  Importance  of  bread  as  an  article  of 
diet.  Antiquity  of  fermented  bread.  Fermentation  not  neces- 
sary to  wholesome  bread.  Aerated  bread  is  a  substitute  for 
the  fermented  article. 


LESSON    XXXII. 

AUXILIARY   FOOD. 

259.  Oils  and  Fats —  their   dietetic   value.  — The 

group  of  oils  and  fatty  substances  forms  an  important 
element  in  the  diet  of  the  inhabitants  of  cold  climates. 
The  animal  tissues  containing  fatty  deposits  are  usually 
subjected  to  the  same  cooking  processes  as  the  fibrous 
meats,  but  the  oil  undergoes  no  change  whatever  in  the 
operation.  This"  class  of  food,  however,  is  not  confined 
to  animal  substances,  but  is  found  extensively  distrib- 
uted through  the  vegetable  kingdom. 

Oil  is  the  most  concentrated  form  of  heat-producing 
food;  therefore  most  appetites  demand  it  in  cold  weather, 
even  in  our  temperate  latitudes.  Its  rapid  combination 
with  the  oxygen  inhaled  by  the  lungs  is  also  an  im- 
portant source  of  vital  force,  and  it  is  on  this  account 
that  persons  engaged  in  severe  labor  in  the  open  air 
demand  oily  food. 

260.  Oily  Food  for  Consumptives.  —  Of  late  it  has 
been   maintained   that   a   deficiency   of  oily   food    pre- 


AUXILIAKY  FOOD.  181 

disposes  to  consumption,  and  a  careful  observation 
of  the  early  habits  of  consumptive  persons  shows  that 
a  very  large  proportion  of  this  class  were  not  in  the 
habit  of  eating  fat  meats,  many  of  them  declining 
even  butter.  Dr.  Carpenter  says:  "There  is  a  strong 
tendency  and  increasing  reason  to  believe  that  a  defi- 
ciency of  oleaginous  matter,  in  a  state  fit  for  appro- 
priating by  the  nutritive  processes,  is  a  fertile  source 
of  diseased  action,  especially  that  of  a  tuberculous 
character;  and  that  the  habitual  use  of  it  in  large 
proportions  would  operate  favorably  in  the  prevention 
of  such  maladies." 

It  is,  however,  an  unsettled  question,  whether  this 
abstinence  from  fatty  food  is  the  came  or  the  effect  of 
the  consumptive  tendency.  Care  should  be  taken  that 
oils,  fats,  and  butter  used  for  food  be  fresh  and  sweet. 
Rancid  fat  or  butter  is  always  unwholesome. 

261.  Salt — its  use  in  the  Animal  Economy. — There 
are  many  substances  which  enter  into  our  daily  bill  of 
fare  which  are  not  properly  food,  and  yet  they  affect 
our  health  in  a  very  important  degree.  Common  salt 
(chloride  of  sodium)  may  with  propriety  be  placed  at 
the  head  of  this  list.  It  has  been  held  by  some  writers 
that  salt  is  not  necessary  to  the  maintenance  of  good 
health,  and  even  that  its  use  is  injurious. 

It  is  true  that  many  savage  tribes,  living  almost 
exclusively  on  animal  food,  have  maintained  good 
health  without  the  use  of  salt;  but  extensive  ob- 
servation proves  that  persons  living  on  a  mixed  diet, 
or  chiefly  on  vegetables,  lose  their  health  when  salt 
is  withheld  from  their  food.  Both  chlorine  and  sodium, 
the  two  elements  of  which  salt  is  formed,  are  essential 


182  HYGIENE. 

to  the  digestion  of  food,  the  former  furnishing  the  acid 
for  the  gastric  fluid,  and  the  latter  the  alkaline  proper- 
ties of  the  bile.  In  flesh-eating  tribes,  these  are  fur- 
nished in  sufficient  quantity  from  the  animal  food  on 
which  they  subsist. 

262.  Salt   retards   Transformation.  —  Salt   has   an- 
other office  in  the  animal  economy.     It  appears  to  be 
a  kind  of  governor,  regulating  the  rate  at  which  the 
changes   in   the   body   proceed.     Salt    is   an    antiseptic, 
and  therefore  retards  the  transformation  of  the  tissues. 
Lean    persons   of   active    habits   have    an    instinct   for 
salt,    and    generally    use    it    freely    with    their    food; 
while  persons  of  full  habit,  or  tending  to  corpulency, 
use  it  but  sparingly,  the  transformation  being  already 
too  slow. 

Pepper  and  other  condiments,  such  as  mustard,  horse- 
radish, etc.,  are  direct  stimulants,  both  on  the  local 
surfaces  with  which  they  come  in  contact,  and  on  the 
general  circulation.  By  their  local  action  they  increase 
the  flow  of  saliva  and  gastric  fluid;  but  the  quality  of 
these  secretions  is  impaired  nearly  in  the  proportion 
that  their  quantity  is  increased,  so  that  really  little  or 
nothing  is  gained  in  the  digestive  process. 

263.  Effect   of  Highly-seasoned  Food.  — The  con- 
tinued and  habitual  use  of  highly-seasoned  food  vitiates 
the   secretions   of  the   mouth    and   stomach,   and   thus 
impairs    digestion;    and   worse    even   than    this,    such 
stimulants   impair   the   sense  of  taste  and  pervert  the 
appetite,  the  natural  faculty  of  selection,  and  the  power 
of  determining  both  the  quantity  and  quality  of  food 
which    the    necessities   of  the   system   demand.     In    a 
healthy  condition,  the  digestive  organs  will  not  require 


AUXILIARY  FOOD.  183 

condiments    to    assist    them    in    the    performance    of 
their  work. 

If  this  is  true  of  pepper  and  kindred  stimulants, 
it  is  more  intensely  important  in  regard  to  wine,  beer, 
and  other  alcoholic  drinks  used  at  meals,  under  the 
pretext  of  creating  an  appetite.  Such  beverages  not 
only  act  as  a  local  irritant  on  the  mucous  membrane 
of  the  stomach,  but  the  effect  of  the  alcohol  is  to  impair 
sensibility  in  the  nerves  of  that  organ,  and  to  disturb 
if  not  suspend  digestion  by  its  well-known  power  of 
preserving  organic  substances  from  decomposition  or 
change. 

264.  Yinegar  —  its  effect  on  Digestion.  —  Vinegar 
is  extensively  used  as  an  auxiliary  food.     It  furnishes 
no  nutriment;    indeed,  it  is  not  digestible;  but  when 
nitrogenous  food    is   taken    in   large   quantities,   or   in 
such  form  as  to  be  difficult  of  digestion,  the  secretion 
of  the    stomach    frequently    fails    to    furnish    the    acid 
quality  of  the  gastric  fluid  sufficiently  to  complete  di- 
gestion before  putrefaction  takes  place.     Vinegar  more 
nearly  supplies   this  defect   than   any  other   substance 
which  could  be  used  with  safety. 

Nitrogenous  vegetables,  such  as  cabbage,  etc.,  are 
rendered  more  digestible  by  vinegar.  Two  precautions, 
however,  are  necessary  in  the  use  of  vinegar:  1st.  We 
should  be  sure  that  it  is  vinegar  that  we  are  using,  as 
many  dangerous  compounds  of  cheap  mineral  acids  are 
sold  for  vinegar;  2d.  The  vinegar  for  the  table  should 
be  largely  diluted  with  water. 

265.  Soda  —  its  use   in   Cooking.  —  Much   has  been 
said  of  the  use  of  soda  in  the  different  culinary  proc- 
esses, and  considerable  alarm  has  been  manifested  over 

B.  P.— 16. 


184  HYGIENE. 

the  constantly  increasing  use  of  this  article.  While  it 
admits  of  no  doubt  that  caustic  soda  is  a  dangerous 
poison,  and  that  even  the  milder  carbonate  is  unfit  to 
be  taken  into  the  stomach  in  that  state,  yet  it  must  be 
remembered  that,  in  cooking,  the  use  of  soda  is  confined 
almost  exclusively  to  the  neutralizing  of  acids  which  it 
is  desirable  to  get  clear  of,  or  as  a  means  of  obtaining 
carbonic  acid  to  lighten  bread  artificially.  In  either 
of  these  instances  the  soda  becomes  a  neutral  salt,  and 
nearly  all  the  salts  of  soda  are  harmless. 

But  it  may  be  well  to  say  that,  though  no  bad  effects 
result  from  the  use  of  well  neutralized  soda,  yet  the 
practice  of  using  it  to  mitigate  the  acid  of  sour  fruits, 
in  cooking  them,  has  the  effect  to  impair  their  flavor 
and  ultimately  to  render  them  insipid. 

266.  The  Appetite— when  it  is  safe  to  follow  it.- 

Before  closing  the  subject  of  the  quality  of  food  as 
affecting  health,  it  will  be  proper  to  state,  in  general 
terms,  that  the  most  reliable  guide  in  selecting  our 
bill  of  fare  is  an  unperverted  appetite.  This,  however, 
is  very  rarely  to  be  found  in  civilized  communities. 
The  false  and  often  pernicious  theories  of  nurses  and 
mothers  too  frequently  establish  wrong  habits  and 
perverted  tastes,  long  before  the  unfortunate  victim 
learns  to  form  a  proper  judgment  by  his  own  reason- 
ing from  physiological  laws;  and  even  then  it  too 
often  happens  that  wrong  habit  is  stronger  than  right 
knowledge. 

Children  naturally  prefer  plain,  simple,  nutritious 
food,  but  if  they  are  fed  on  that  which  is  highly- 
seasoned  and  stimulating,  accompanied  with  wine  or 
other  narcotic  beverages,  plain  food  will  soon  fail  to 


QUANTITY  OF  FOOD.  185 

gratify  their  desires.     The  appetite  is  then  an  unsafe 
guide. 

Recapitulation. 

Oils  and  fats  are  demanded  in  cold  climates,  and  in  the 
winter  season  of  temperate  climates.  Their  necessity  in  the 
diet  of  those  predisposed  to  consumption.  Salt  furnishes  the 
chlorine  and  soda  necessary  for  healthy  action  of  the  system. 
It  retards  transformation  of  the  tissues.  Highly-seasoned  food 
and  stimulating  condiments  are  injurious.  Vinegar  hastens  the 
digestion  of  nitrogenous  food.  Soda,  when  used  in  cooking, 
should  always  be  neutralized  by  an  acid.  An  unperverted 
appetite  is  the  best  guide  in  the  selection  of  food. 


LESSON   XXXIII. 

QUANTITY  OF   FOOD. 

267.  Quantity  of  Food.  —  The  quantity  of  food 
necessary  to  the  maintenance  of  good  health  has  been 
variously  stated  by  different  authors.  Indeed,  there 
are  so  many  modifying  circumstances  connected  with 
this  question,  that  no  definite  statement  can  be  made 
that  will  be  in  any  degree  reliable.  Age,  sex,  tem- 
perament, occupation,  state  of  health,  and  previously 
established  habits,  each  exerts  a  greater  or  less  influ- 
ence on  the  demands  of  the  system  for  support. 

Dr.  Dalton  says  that  a  man  in  full  health,  living  on 
a  diet  exclusively  of  bread,  butter,  and  meat,  with  coffee 
and  water  for  drink,  and  exercising  in  the  open  air, 
will  require,  in  each  twenty-four  hours,  nineteen  ounces 


186  HYGIENE. 

of  bread,  three  and  one-half  ounces  of  butter,  and  six- 
teen ounces  of  meat,  with  fifty-two  ounces  of  drink. 
The  army  rations  of  the  United  States  soldier  exceed 
Dalton's  estimate  by  about  twenty  per  cent,  besides 
adding  rice,  sugar,  and  beans  to  the  bill  of  fare.  The 
rations  in  European  armies  are  somewhat  less  than 
this. 

268.  Digestion  modifies  Food.  —  The  more   or  less 
perfect    manner    in    which    the    digestive    process    is 
performed,   is   a   modifying   circumstance  to  which   too 
little    importance    has    been    attached.      Two    persons, 
each   in   good   health,  of  the   same   age,  and  following 
the  same  occupation,  will  eat  equal  quantities   of  the 
same  kind  of  food,  and  yet  derive  nutriment  from  it 
in  very  different  proportions. 

It  is  not  the  quantity  of  food  taken,  but  the  amount 
digested,  which  ministers  to  the  support  of  the  living 
body.  This  defective  digestion  may  depend  on  a  nat- 
ural debility,  a  lack  of  vital  force  in  the  organs  con- 
cerned in  the  work ;  but  more  frequently  it  is  the  result 
of  bad  habit,  the  habit  of  overeating,  formed  in  early 
life.  As  the  digestive  process  will  seldom  take  from 
the  food  more  nutriment  than  the  demands  of  the 
system  require,  so  when  that  amount  is  obtained  the 
work  is  suspended,  and  the  residue  is  passed  off  as 
waste  matter. 

269.  Use    of    Tobacco.  —  Persons    addicted    to    the 
use    of    tobacco    require    a   larger    amount    of   food    to 
furnish  the  same  nutrition  than   persons   who  do  not 
use    the    narcotic.     The    saliva,    being    rendered    unfit 
for  its   office,  is   wasted,   and   the   starchy   part   of  the 
food,    which    should    have   been   converted    into   sugar 


QUANTITY   OF  FOOD.  187 

by  this  fluid,  remains  to  a  great  extent  unchanged. 
The  saliva  is  less  important  in  the  digestion  of  animal 
food,  and  for  this  reason  those  who  use  tobacco  in- 
stinctively become  largely  flesh-eaters,  or  the  habit 
induces  dyspepsia. 

Alcoholic  drinks  produce  similar  effects,  by  impairing 
the  sensibility  of  the  stomach,  and  diminishing  its  vital 
force.  By  these  derangements  the  stomach  permits  the 
imperfectly  digested  food  to  pass  the  pyloric  orifice,  and 
so  but  a  small  amount  of  its  nutriment  is  made  availa- 
ble. The  appetite  demands  more  food,  and  this  morbid 
and  pernicious  effect  of  the  "  bitters  "  is  often  mistaken 
for  an  evidence  of  increased  nutrition. 

270.  Temperature  —  its  influence  on  Food.  —  A  few 

general  principles,  judiciously  applied,  will  be  found 
more  effectual  in  regulating  the  quantity  of  food  than 
any  special  rules  that  can  be  laid  down.  In  childhood 
and  youth,  the  nutrition  must  not  only  supply  the 
waste  of  the  system  —  which  is  greater  in  a  given  time 
than  in  adult  age  —  but  also  a  surplus,  to  be  applied  to 
growth. 

In  cold  weather  the  transformation  of  the  tissues  is 
more  rapid,  and  a  greater  amount  of  heat-producing 
food  is  consumed  to  maintain  the  temperature  of  the 
body.  The  amount  of  this  increase  will  be  modified  by 
circumstances.  Persons  w'ell  provided  with  warm  cloth- 
ing, living  in  comfortable  houses,  and  spending  their 
time  chiefly  in  well-warmed  apartments,  will  scarcely 
require  any  increase  of  food;  but  the  poorly  clad  and 
housed,  and  those  engaged  in  out-door  occupations, 
will  require  their  food  to  be  greatly  augmented  in 
cold  weather. 


188  HYGIENE. 

271.  Exercise  and  Ventilation  vary  the  quantity 
of  Food.  —  Active  muscular  exercise  draws  largely  on 
the  vital  force;  but  the  evolution  of  force  is  intimately 
connected  with  the   wastes  of  the  body,  the  oxidation 
of  the  food  we  digest,  and  of  the  worn-out  particles  of 
the  body.     These  wastes  must  find  an  appropriate  com- 
pensation in  an  increase  of  food.     If  the  exercise  be  in 
the  open  air,  the  atmosphere   pure,  and  the  breathing 
free,  the  increased  demand  for  food  will  be  much  greater 
than  if  the  same  exercise  had  been  taken  in  a  close,  ill- 
ventilated  room. 

But  the  force  furnished  to  perform  the  exercise  or 
labor  will  be  in  the  exact  proportion  of  the  wastes  to  be 
supplied,  and  if  the  demand  for  food  is  not  increased, 
the  ability  to  perform  the  exercise  will  soon  fail.  From 
this  cause  persons  are  capable  of  performing  more  severe 
and  longer  protracted  labor  in  the  open  air  than  in 
badly-ventilated  rooms. 

272.  Change  of  Habits  demands  change  in  Food.  — 

In  altering  their  habits  of  life,  persons  should  be  care- 
ful to  adapt  the  quantity  of  food  to  the  modified  condi- 
tion. If  the  change  be  from  sedentary,  in-door  occupa- 
tion to  active,  open-air  labor,  the  appetite  will  generally 
point  out  the  proper  alteration  in  diet;  but  changes  in 
the  opposite  direction  are  not  so  promptly  indicated, 
or,  if  so,  the  indications  are  not  always  heeded. 

Pupils  leaving  the  active  employments  of  the  farm, 
and  confining  themselves  to  the  school-room,  often  injure 
their  health  by  continuing  the  same  diet,  both  in  quan- 
tity and  quality,  which  they  found  necessary  when 
engaged  in  daily  labor.  After  a  careful  attention  to 
this  subject  for  the  first  week  of  school  life,  it  may  be 


QUANTITY  OF  FOOD.  189 

safely  intrusted  to  the  appetite.  Persons  making  such 
a  change  of  habits  are  frequently  alarmed  at  their 
failing  appetite,  and  resort  to  medicines  to  provoke 
a  desire  for  food.  This  is  all  wrong. 

273.  Mental  Labor — the  diet  it  demands. — Pupils 
at  school,  and  other  persons  engaged  in  mental  labor, 
need  a  plain,  liberal  diet.     The  amount  of  food  devoted 
to  muscular  repair  and  the  production  of  animal  heat 
should  be   reduced  proportionally  to  their   diminished 
physical 'exercise,  yet   it  by  no  means  follows  that  it 
is  necessary  to  starve  the  body  to  invigorate  the  mind. 
This  hypothesis,  so  popular  a  few  years  ago,  has  been 
superseded  by  more  rational  views. 

Brain  is  exhausted  by  activity  even  more  rapidly 
than  muscle,  and  the  waste  of  its  material  is  propor- 
tionally great.  To  replace  this  wasted  matter  requires 
a  full  supply  of  food,  rich  in  albumen  and  the  phos- 
phates. Eggs,  fish,  oysters  and  other  shell-fish,  the 
lean  part  of  mutton  and  beef,  and  wheat  bread,  are 
all  articles  rich  in  brain  elements,  and  may  be  used 
liberally  if  cooked  plainly,  with  no  other  seasoning 
than  salt.  Fruits,  either  raw  or  cooked  by  stewing  or 
baking,  may  be  introduced  as  dessert. 

274.  Bribing   the   Appetite.  —  The   appetite   is   the 
only  measure  to  determine  the  quantity  of  food  to  be 
taken,  but  many  devices  have  been  invented  to  bribe 
the  appetite  to  take  more  food  than  the  demands  of 
the  system  require,  or  to  take  it  when  none  is  needed. 
Highly-seasoned  food  perverts  the  appetite,  and  renders 
it  an  unsafe  guide.     A  great  variety  of  dishes  at  the 
same  meal  has  the  same  effect. 

A  single  course,  consisting  of  one  kind  of  meat  or 


190  HYGIENE. 

eggs,  one  variety  of  vegetables,  with  bread  and  butter., 
and  some  palatable,  unstimulating  diet  drink,  in  very 
moderate  quantities,  will  furnish  a  meal  which  may  be 
supplemented  by  a  dessert  of  fruit.  Of  such  a  repast, 
the  appetite  will  determine  very  accurately  when  to 
desist  from  eating.  A  person  should  never  suffer  him- 
self to  be  decoyed  into  taking  food  when  there  is  no 
desire  for  it. 

Recapitulation. 

The  quantity  of  food  demanded  to  supply  the  wastes  of  the 
system  depends  primarily  on  its  perfect  digestion.  Tobacco 
and  alcohol  impair  digestion.  Temperature  modifies  the  de- 
mand for  food.  A  change  of  habits  of  life  requires  a  corre- 
sponding variation  in  diet.  Exercise  and  good  ventilation  in- 
crease the  demand  for  food.  Brain  labor  needs  a  generous 
diet.  The  use  of  highly-seasoned  food  renders  the  appetite 
an  unsafe  guide. 


LESSON    XXXIV. 

TIME   OF   TAKING    FOOD. 

275.  Intervals  at  which  Food  should  be  taken. — 

Food  should  be  taken  at  such  intervals  as  will  permit 
the  stomach  to  perform  the  labor  of  digestion,  and  en- 
joy a  period  of  rest  about  equal  to  the  time  of  its 
active  work.  An  ordinary  meal,  in  a  healthy  stomach, 
will  be  disposed  of  in  about  three  hours;  and  if  we 
allow  the  same  time  for  rest,  this  will  make  an  inter- 
val of  six  hours  between  meals. 

Nearly  all   civilized   nations   have   adopted   the   rule 


TIME  OF  TAKING  FOOD.  191 

of  three  meals  per  day — a  few,  more  than  this,  and 
some,  less.  But  individuals  are  found,  in  all  commu- 
nities, who  depart  from  the  general  usage  of  society  in 
one  direction  or  another. 

Whatever  rule  is  adopted,  it  should  be  made  a  uni^ 
form  habit,  which  should  not  be  violated  except  under 
the  most  urgent  necessity.  When  a  habit  is  fully 
established,  the  quantity  of  food  will  not  depend  on 
the  number  of  meals.  A  person  eating  but  once  in 
twenty-four  hours  will  take  as  much  food  at  that  one 
meal  as  he  would  take  if  it  were  divided  into  three 
meals. 

276.  Early  Breakfast — why  required. — WThen  three 
meals  are  taken,  the  morning  one  should  come  early, 
or  at  least  before  we  enter  on  any  of  the  active  duties 
of  the    day.     The   long    interval    between    supper   and 
breakfast  is  or  should  be  an  interval  of  rest,  yet  the 
active  absorbents  have  carried  into  the  circulation,  in 
this  time,  all  the  nutritious  matter  derived  from  yester- 
day's food,  and  the  stomach  is  now  in  an  empty  con- 
dition, awaiting  a  fresh  supply.     Any  heavy  drafts  on 
the  vital  force  in  this  condition  can  not  fail  to  seriously 
disturb  the  equilibrium  of  that  force,  and  derange  im- 
portant functions. 

In  this  state,  the  system  demands  that  the  digestive 
apparatus  should  be  early  set  at  work  to  prepare  nutri- 
ment sufficient  to  meet  the  heavy  drafts  of  a  day  of 
active  exertion.  This  view  of  the  subject  demands 
that  breakfast  should  be  a  substantial  meal  of  good, 
nutritious  food. 

277.  Dinner — its  proper  time.  —  Dinner  should  not 
be  delayed  much  beyond  six  hours  after  the  morning 

r>.  P. -17. 


192  HYGIENE. 

meal.  Late  dinners  require  that  the  interval  between 
them  and  the  evening  meal  be  too  short,  or  that  the 
latter  be  crowded  too  close  to  the  hour  of  retiring  for 
sleep.  If  the  meals  be  taken  at  regular  intervals  of 
six  hours,  beginning  at  about  seven  o'clock  in  the 
morning,  they  may  all  be  made  full  meals  of  sub- 
stantial food;  but  if  the  dinner  be  delayed  till  four 
o'clock  in  the  afternoon,  the  evening  meal,  if  not  en- 
tirely dispensed  with,  should  be  very  light  both  in 
quantity  and  quality,  and  should  be  taken  not  later 
than  eight  o'clock. 

Late  suppers  of  heavy,  indigestible  food  are  a  fruit- 
ful source  of  dyspepsia,  and  that  long  train  of  nervous 
diseases  which  render  life  an  intolerable  burden  to  so 
many.  No  food  should  be  taken  nearer  than  two 
hours  to  the  time  of  retiring,  and  that  time  should  not 
be  later  than  ten  o'clock. 

278.  Eating  between  Meals — its  pernicious  effects. — 

The  practice  of  eating  "pieces"  between  meals  is  a 
most  pernicious  habit,  and  one  that  is  the  prolific 
cause  to  which  may  be  traced  the  ruin  of  so  many 
constitutions,  even  in  childhood.  •  When  food  is  taken, 
a  full  meal  should  be  made,  and  the  stomach  should 
then  be  permitted  to  digest  it  without  disturbance. 
But  if  fresh  portions  of  food  be  introduced  when  the 
stoniach  has  half  finished  its  work,  the  result  is  that 
neither  portion  is  properly  digested;  for  the  process 
is  thereby  prolonged,  the  stomach  is  virtually  kept  at 
constant  labor,  and  its  powers  are  so  enfeebled  and 
exhausted  that  it  fails  to  provide  the  means  of  nu- 
trition sufficient  to  supply  the  demands  of  the  system, 
or  to  compensate  for  its  daily  waste. 


TIME  OF  TAKING  FOOD.  193 

Loss  of  appetite  and  general  debility  ensue,  followed 
by  a  train  of  nervous  derangements  that  disturb  all 
the  vital  functions.  Half  the  ruined  constitutions, 
that  are  not  traceable  to  alcohol  and  tobacco,  may 
safely  be  referred  to  the  habit  of  eating  between 
meals. 

279.  Meals  should   not   be   interrupted.  —  Eating 
should  be  done  slowly  and  deliberately,  but  it  should 
also  be   done   continuously.     By   this   we  mean   that, 
when    a    meal    is    begun,    it    should    proceed   without 
any  considerable  interruption  to  its  termination.     The 
stomach  does  not  begin  the  process  of  digestion  till  eat- 
ing is  finished;  but  if,  after  the  first  course  at  a  fashion- 
able dinner,   there    is   an    interval   of   ten  minutes,   a 
healthy  stomach  will  go  promptly  to  work  on  the  food 
already  taken.     But   this   will   be    interrupted   by  the 
second  course,  and  the  stomach,  thus  disturbed,  will  re- 
turn to  its  task  tardily,   and  will  be   likely  to  do   its 
work  imperfectly. 

Extremes  of  temperature  in  our  food  should  be 
avoided.  Food,  to  be  promptly  digested,  must  vary  but 
a  few  degrees  from  blood-heat.  Hot  food  and  drink,  or 
ice-water,  ice-cream,  etc.,  taken  into  the  stomach,  sus- 
pend all  action  till  the  mass  has  acquired  the  tempera- 
ture of  the  body.  (§  224.) 

280.  Importance  of  thorough  Mastication.  —  Good 
health  depends  not  alone  on  what  we   eat,  and  when 
we  eat  it,  but  the  manner  of  taking  food  is  of  the  first 
importance  in  this  relation.     Eating,  as  we  have  said, 
should  be  done  slowly  and  deliberately,  and  the  masti- 
cation   should  be   thorough.     This    is   demanded   more 
especially  with  regard   to   the  starchy  forms  of  food. 


194  HYGIENE. 

Saliva  is  the  immediate  agent  by  which  starch  is 
changed  into  sugar,  and  thus  rendered  soluble  and 
transformed  into  available  nutriment. 

But  if  the  food  be  hurried  through  the  mouth,  and 
but  imperfectly  mixed  with  saliva,  the  digestion  will 
be  equally  imperfect,  and  much  o£  the  nutriment  lost. 
A  worse  defect  in  mastication  than  this  occurs  when, 
by  the  use  of  tobacco,  the  saliva  is  poisoned  and  ren- 
dered unfit  for  the  purposes  of  mastication;  or  the 
salivary  glands,  goaded  to  constant  overaction,  secrete 
a  fluid  which  contains  none  of  the  essential  properties 
of  saliva,  and  therefore  can  not  aid  in  digestion. 

281.  Good  Teeth  necessary  to  Mastication.  —  The 

grinding  of  food,  the  mechanical  work  of  mastication, 
is  performed  by  the  teeth ;  and  in  order  that  the  work 
should  be  well  done,  the  machinery  should  be  kept  in 
good  order.  But,  in  this  country,  a  good,  sound  set  of 
teeth,  in  a  middle-aged  person,  is  rare.  Many  things 
have,  each  in  their  turn,  been  charged  with  causing 
the  premature  decay  of  teeth,  so  common  and  so  dam- 
aging to  good  health. 

It  is  pretty  clear  that  the  mischief  is  traceable  to  a 
combination  of  causes  rather  than  to  any  one  agent. 
The  teeth  are  covered  with  an  enamel  which,  if  prop- 
erly taken  care  of,  will  protect  them  from  the  chemical 
action  of  any  thing  proper  to  be  taken  into  the  mouth ; 
but  this  enamel  may  be  broken,  either  by  mechanical 
means,  or  by  taking  food  too  hot  or  too  cold,  and  decay 
will  inevitably  follow. 

282.  Rules  for  preserving  the  Teeth.  —  The  pres- 
ervation of  the  teeth  is  a  subject  of  too  much  impor- 
tance to  be  passed  over  lightly;  we  therefore  submit  a 


TIME  OF  TAKING  FOOD.  195 

few  general  rules  for  their  care.  After  eating,  the  teeth 
should  be  thoroughly  cleaned,  removing,  by  means  of  a 
tooth-pick  of  wood,  quill,  or  ivory,  whatever  has  lodged 
between  them,  and  washing  the  mouth  with  tepid  water. 
Never  use  a  metallic  instrument  of  any  kind  to  clean 
the  teeth,  for  in  its  use  there  is  always  a  liability  to 
fracture  the  enamel,  which  is,  of  all  things,  most  to  be 
guarded  against. 

All  tooth-powders  and  dentifrices  are  to  be  avoided, 
for  even  the  constant  rubbing  of  the  teeth  with  pow- 
dered charcoal  will  ultimately  wear  through  the  enamel, 
and  expose  the  teeth  to  decay.  A  soft  brush,  a  little 
fine  soap,  and  soft  water  about  blood-heat,  will  cleanse 
the  teeth  more  thoroughly  and  more  safely  than  the 
most  expensive  dentifrice. 

• 

Recapitulation. 

Three  meals  a  day  generally  adopted  in  civilized  countries. 
Meals  should  be  taken  at  intervals  of  at  least  six  hours. 
Breakfast  should  be  eaten  before  commencing  the  day's  labor. 
Late  dinners  bring  the  evening  repast  too  near  the  hour  of 
retiring.  The  pernicious  effects  of  late  suppers.  Eating  be- 
tween meals  is  a  fruitful  source  of  indigestion.  The  digestive 
apparatus  must  have  time  to  rest.  Meals,  when  once  begun, 
should  not  be  interrupted.  Care  of  the  teeth  important  to 
good  health. 


196  HYGIENE. 


LESSON   XXXV. 

CONDITION   OF   THE    SYSTEM. 

283.  Do   not   eat   when   fatigued.  —  The   condition 
of  the    system,   at   the   time   of  taking    and    digesting 
food,  is  a  matter  not  to  be  overlooked  in  the  hygiene 
of  nutrition.     To  digest  a  full   meal,  is   an   operation 
which   draws   heavily  on  the   nervous   system   for   the 
force    necessary   to    maintain    the    constant    motion    of 
the  stomach,  by  which    its   contents   are   moved  about 
so  that   every   part  of  it   may   be   brought    in   contact 
with  the    surface    secreting   the   gastric   fluid,  as  well 
as  to  keep  up  a  full  flow  of  this  secretion. 

Now  if  labor  of  muscle  or  mind  has  been  carried  to 
fatigue,  and  a  feeling  of  exhaustion  is  experienced,  it 
would  be  very  improper  to  take  food  until  the  ex- 
hausted vital  force  has  been  restored  by  rest.  Persons 
engaged  in  active  labor,  or  in  hard  study,  should  allow 
themselves  at  least  half  an  hour  for  rest  of  body  and 
mind  before  assigning  to  the  stomach  its  task  of  digest- 
ing a  meal. 

284.  Rest   should  follow  Meals.  —  It  is  equally  im- 
portant that  an  interval  of  rest  and  relaxation  should 
follow  each  meal.    The  action  of  the  stomach  is  invol- 
untary, and   proceeds  without   our    knowledge   or   con- 
sent;   yet,  if   a  strong   effort  be  made  to  carry  on   any 
voluntary  function,  the  vital   force  will  be  directed  to 
the   organs   concerned   in   that   work,  and    being   thus 
turned  away  from  the  stomach  the   work  of  digestion 
can  not  proceed  for  want  of  power. 


CONDITION  OF  THE   SYSTEM.  197 

It  is  not  merely  vigorous  muscular  exertion  which 
produces  this  effect,  but  it  may  be  even  more  certainly 
induced  by  brain  labor.  Some  of  the  most  inveterate 
cases  of  indigestion  are  traceable  to  the  habit  of  spend- 
in<r  the  dinner  hour  in  reading  and  hard  study.  This 
is  a  habit  which  laboring  men,  anxious  both  to  acquire 
knowledge  and  economize  time,  are  apt  to  fall  into,  and 
against  which  they  should  be  warned. 

285.  Cheerfulness  during  Meals. — A  lively,  cheerful 
state  of  mind,  as  far  as  this  can  be  commanded,  should 
accompany    all    our    meals;     and    if    the    surrounding 
circumstances   force   on   us   the   melancholy   mood,  our 
meals  should  consist  of  light,  digestible  food,  in  small 
quantities.     Under    such    circumstances    the    appetite 
will    seldom    demand    food;    and    care    must    be    taken 
that  we  are  not  decoyed  into  the  mistake  of  attempt- 
ing  to  create   an   appetite   by  local    stimulants,   or   of 
escaping  from   the   cares  that  oppress   us  by  a   resort 
to  alcoholic   exhilarants. 

At  least  half  an  hour  should  be  spent  in  sprightly 
conversation  or  amusement  after  a  meal  is  taken. 
Light  reading,  which  will  amuse  and  entertain,  will 
furnish  a  safe  means  of  passing  this  interval  between 
eating  and  business. '  But  works  of  fiction  which  appeal 
strongly  to  the  imagination  or  rouse  emotions  should 
be  carefully  avoided. 

286.  Rest  after  Meals  —  objection  to  the  Siesta.— 
The   half    hour    of   rest    after    meals,  which   we    have 
recommended,  will   be    sufficient,   ill    most    persons,  to 
start  the  process  of  digestion;    and  when  the  stomach 
1ms  become  fully  engaged  in  its  work,  it  will  not   be 
easily    diverted    from    it.     But    on    resuming    business 


198  HYGIENE. 

we  should  begin  moderately,  and  not  tax  our  powers 
to  their  full  capacity  for  at  least  the  first  hour  of 
labor.  When  the  time  can  be  spared,  it  will  be 
safer  to  lengthen  the  period  of  rest  after  eating  to 
an  hour,  which  could  be  economized  by  devoting  it 
to  some  easy  task  that  will  but  lightly  tax  either 
muscle  or  brain. 

To  the  Spanish  siesta,  or  hour  of  sleep  after  dinner, 
there  is  a  physiological  objection.  All  the  vital  powers 
are  depressed  during  sleep,  and  the  stomach  feels  this 
lowering  of  vital  force  in  common  with  all  the  other 
organs,  and  consequently  digestion  can  not  be  perfectly 
performed. 

287.  Food  not  to  be  taken  when  there  is  no  Appe- 
tite.— We  have,  in  a  previous  lesson,  intimated  that 
food  should  be  taken  at  regular  intervals,  and  this 
regularity  should  be  maintained  till  it  grows  into  a 
habit.  This,  however,  is  to  be  accepted  under  certain 
restrictions.  There  are  conditions  of  the  system  in 
which  the  appetite  does  not  ask  for  food,  and  in 
which  to  take  food  into  the  stomach  would  only  add 
a  new  source  of  irritation,  which  might,  with  existing 
disturbances,  prove  a  cause  of  serious  sickness. 

These  conditions  may  be  reduced  to  two  general 
divisions,  to  wit :  Those  in  which  the  loss  of  appetite 
springs  from  derangements  in  the  digestive  apparatus, 
so  that  food,  if  taken,  could  not  be  properly  digested, 
and,  by  becoming  either  acid  or  putrid  in  the  stomach, 
would  not  fail  to  seriously  irritate  that  organ;  and 
those  in  which  the  loss  of  appetite  arises  from  dimin- 
ished wastes  of  the  system,  reducing  the  demand  for 
nutrition. 


CONDITION  OF  THE  SYSTEM.  199 

288.  Abstinence  —  when  necessary.  —  The  first  of 
these  conditions,  resulting  in  a  loss  of  appetite,  usually 
has  its  origin   in   improper   eating  as  to  the  quantity 
of  food,  its  quality,  or  the  time  of  taking  it.     Under 
these    circumstances   nothing   more    is    necessary   than 
to  abstain  from  eating  and  await  a  return  of  appetite. 
If  there  be  no  serious  disease  approaching,  abstinence 
from   food   for  twenty-four  hours   will  correct   the  dis- 
turbance and  bring  a  renewed  appetite. 

The  second  condition  may  generally  be  traced  to  a 
lack  of  active  exercise  in  the  open  air.  When  the 
change  or  transformation  of  the  tissues  is  retarded, 
the  demand  for  new  material  is  proportionally  dimin- 
ished, and  the  digestive  organs  refuse  to  prepare  nutri- 
tion beyond  the  healthy  demands  of  the  system. 

289.  Efforts   to   create   an   Appetite.  —  The   habit 
of   urging    food  on   invalids   when   there    is    no   desire 
for    it,   is    only   equaled   in   absurdity   by  the   opposite 
error   of   denying   food   to   convalescent    persons   when 
the   appetite    imperiously   demands   it.     In    these    con- 
ditions of  the  system,  which    disqualify  the   digestive 
apparatus  for  the   performance  of  its  proper  office,   it 
is  a  very  grave  mistake  to  resort  to  medicines  to  create 
an  artificial  appetite. 

When  we  look  at  the  formidable  catalogue  of  tonics, 
and  bitters,  and  other  nostrums,  with  which  the  public 
regularly  doses  itself,  and  all  for  the  purpose  of  provok- 
ing an  appetite  against  the  wiser  instincts  of  the  sys- 
tem, it  is  surprising  that  comparatively  so  little  mis- 
chief is  done  by  all  this  war  on  nature.  Out  of  this 
injudicious  tampering  with  the  digestive  organs  grow 
most  of  the  chronic  diseases,  which  make  so  many 


200  HYGIENE. 

invalids,  and  induce  premature  old  age  in  so  many 
cases. 

290.  Habits  measure  the  quantity  of  Food.— The 

condition  of  the  system,  with  regard  to  activity  or 
rest,  must  modify  our  diet  both  as  to  quantity  and 
kind;  and  it  will  be  wise  to  depart  even  from  the 
general  rule  of  following  the  appetite  when  changes 
in  manner  of  life  are  suddenly  made,  especially  if  the 
change  be  from  active  labor  to  absolute  rest.  Under 
these  circumstances,  it  will  be  prudent  to  leave  the 
table  while  there  is  still  a  desire  for  more  food. 

The  changes  of  the  season  demand  a  corresponding 
change  in  our  bill  of  fare.  Oils  and  animal  flesh  may 
be  taken  freely  in  winter,  if  we  follow  out-door  occupa- 
tions, but  when  the  relaxing  days  of  spring  come,  we 
should  keep  lent,  for  health,  if  from  no  other  motive. 
Never  take  food  late  at  night  when  the  system  is 
oppressed  with  a  feeling  of  drowsiness  or  languor. 

Recapitulation. 

Food  should  not  be  taken  when  there  is  fatigue  of  either 
muscle  or  brain.  Meals  should  be  followed  by  rest.  Cheerful- 
ness and  mental  relaxation  at  meals  are  important.  Sleep 
should  not  be  indulged  in  during  digestion.  Food  is  not  to  be 
taken  when  there  is  no  desire  for  it.  Abstinence  from  food — 
when  proper,  and  to  what  extent.  Efforts  to  create  an  arti- 
ficial appetite  are  injurious.  Change  of  habits  or  of  season 
demand  a  corresponding  change  of  diet. 


CIRCULATION.  201 

LESSON   XXXVI. 

CIRCULATION. 

291.  Sympathetic  Relations  of  the  Heart  and  Blood- 
vessels.— The  circulatory  apparatus   has  an  extensive 
range  of  sympathies,  being   affected,  more  or  less,  by 
every  change  which  takes  place  in  any  of  the  impor- 
tant organs  of  the  body;   but  the  circulation  is  subject 
to  fewer  direct   disturbances   than  any  other  function 
of  the  living  body. 

The  heart,  the  central  organ  of  the  circulation,  is  so 
situated  that  it  is  removed  from  liability  to  injury  by 
external  accidents;  and  being  an  involuntary  organ, 
the  will  exerts  no  direct  control  over  it,  and  therefore 
it  is  not,  like  the  stomach,  liable  to  be  overworked  for 
any  present  gratification,  or  neglected  in  the  hurry  and 
press  of  other  business.  Nearly  all  the  diseases  to 
which  the  heart  and  blood-vessels  are  subject,  have 
their  origin  in  their  sympathetic  action  with  the 
digestive  or  respiratory  functions,  or  with  the  brain 
.and  nervous  system.  \ 

292.  Pressure  on  the  Yeins.  —  The   veins   perform 
the    work    of   returning   the   blood   to   the    heart,  and 
are   therefore    an    important    link    in    the    process    of 
circulation.     These  are  largely  distributed  on  the  su- 
perficial parts  of  the  body,  and  are  therefore  peculiarly 
subject  to  external  influences,  such  as  change  of  tem- 
perature, mechanical  pressure,  etc.     Moreover  the  veins, 
unlike  the  arteries,   have   soft   and   yielding  coats,  af- 
fected by  the  lightest  pressure;  and  as  the  current  of 
blood  flowing   through   them   is  not  impelled   by  any 


202  HYGIENE. 

direct  active  force  behind  it,  therefore  it  is  more  liable 
to  disturbances  from  external  causes. 

If  the  clothing  is  so  tight  as  to  produce  any  sensible 
pressure,  it  will  retard  the  return  of  venous  blood,  and 
will  to  that  extent  disturb  the  circulation.  Tight  gar- 
ters are  a  fruitful  source  of  cold  feet,  which  so  many 
complain  of.  The  return  of  blood  from  the  feet  being 
interrupted,  the  supply  will  be  diminished  in  propor- 
tion. 

293.  Compression  of  the  Jugular  Teius.  —  A  more 
dangerous  compression  of  the  venous  circulation  is  that 
occasioned   by  tight    collars  or   neckties.     The  jugular 
veins,    which    return    the    blood    from    the    head,    are 
situated  immediately  under  the  skin,  on  each  side  of 
the  neck,  and  are  therefore  very  liable  to  compression 
from  dressing  the  neck  tightly.     Compression  of  these 
vessels    produces    engorgement    of   the    whole    vascular 
system  of   the    brain,   manifesting    itself   by   dizziness, 
a  sense  of  fullness  in  the  head,  or  severe  headache. 

This  will  derange  the  mental  machinery,  and  disturb 
all  the  functions  of  the  nervous  system.  If  the  com- 
pression is  considerable,  and  any  active  exertion  is 
attempted,  the  engorgement  of  the  brain  is  liable  to 
terminate  in  apoplexy;  but  if  the  compression  be 
moderate  and  long  continued,  the  consequence  will  be 
that  less  blood  will  be  sent  to  the  brain,  and  the  whole 
nervous  system  will  be  correspondingly  weakened. 

294.  Muscular  Exercise  and  the  Circulation. — But 

the  circulation  is  affected  indirectly  by  nearly  all  the 
activities  of  the  body.  Every  contraction  of  a  muscle 
makes  momentary  pressure  on  the  veins  in  contact 
with  it,  and  thus  their  contents  are  forced  forward 


CIRCULATION.  203 

in  the  direction  of  the  heart,  the  valves  preventing 
the  flow  in  the  opposite  direction.  The  relaxtion  of 
the  muscle  permits  the  veins  to  fill  again,  and  thus 
the  action  of  the  muscular  system  increases  the 
quantity  of  blood  returned  to  the  heart  in  a  given 
time. 

This  demands  a  more  vigorous  action  of  the  heart, 
and,  under  this  influence,  the  pulse  becomes  fuller, 
stronger,  and  more  frequent.  This  increase  of  circu- 
lation by  exercise  is  a  healthy  action,  and  with  it  an 
increased  respiration  is  demanded  for  the  full  supply  of 
oxygen,  in  order  to  break  down  and  render  soluble  the 
old  material  of  the  tissues,  that  it  may  be  removed  by 
the  absorbents. 

295.  Changes  of  Temperature.  —  The  temperature 
of  the  body  and  the  circulation  of  the  blood  mutually 
affect  each  other.  Whatever  excites  the  circulation, 
and  induces  a  greater  transmission  of  blood  through 
the  capillaries,  increases  the  temperature  in  the  same 
proportion ;  and,  on  the  other  hand,  if  any  part  of  the 
body  be  exposed  to  a  very  low  temperature,  the  vessels 
will  be  contracted,  and  the  circulation  in  that  part 
diminished. 

This  may  be  general,  as  in  a  cold  bath ;  or  local,  as  in 
the  application  of  ice  to  any  part  of  the  body.  But 
when  there  is  a  depression  of  the  circulation  from 
sudden  exposure  to  cold,  there  is  always  an  effort  of  the 
system  to  overcome  the  obstruction  by  augmenting  the 
force  of  the  circulating  current.  Under  these  circum- 
stances, if  the  depressing  cause  be  removed,  the  tem- 
perature suddenly  restores  itself  and  even  rises  above 
its  former  standard;  and  the  increased  action  of  the 


204  HYGIENE. 

capillary  circulation  will  be  maintained  for  several 
hours. 

296.  Change  from  Cold  to  Heat,  most  dangerous.  — 

But  in  feeble  health  this  reaction  does  not  always  take 
place,  especially  if  the  low  temperature  be  long  en- 
dured. Persons,  therefore,  of  feeble  vitality  should  be 
cautious  in  exposing  themselves  to  a  low  temperature, 
whether  in  the  bath,  or  in  a  cold  atmosphere ;  and  they 
should  bear  in  mind  that  the  reactive  force  diminishes 
with  the  length  of  the  exposure. 

The  increased  force  of  the  circulation,  whether  from  a 
high  temperature  of  the  surrounding  medium,  or  from 
violent  and  long-continued  exertion,  is  more  to  be 
dreaded  as  a  cause  of  disease  than  exposure  to  a  k>w 
temperature.  Changes  of  weather  from  cold  to  warm 
are  more  unfavorable  to  health  than  those  in  the  oppo- 
site direction.  By  the  increased  vascular  action  there  is 
induced  a  tendency  to  inflammatory  diseases. 

297.  Influence  of  the  Mind  on  the  Circulation. — 

The  action  of  the  heart  is  readily  influenced  by  the 
mental  condition.  A  powerful  exertion  of  the  purely 
intellectual  faculties,  as  in  the  solution  of  some  in- 
tricate problem,  reduces  both  the  force  and  fullness  of 
the  circulation,  while  the  action  of  the  heart  becomes 
more  frequent,  and  often  irregular. 

Anger  and  the  other  exciting  passions  increase  the 
force  of  the  heart's  action  sometimes  to  an  alarming 
extent.  The  depressing  passions,  such  as  sorrow  or 
grief,  render  the  pulse  empty,  slow,  and  feeble.  Under 
the  influence  of  these  depressing  passions,  the  power 
to  resist  disease  is  greatly  diminished,  as  was  demon- 
strated when  cholera  visited  our  cities  a  few  years  since. 


CIRCULATION.  205 

The  condition  of  the  circulation  is  the  best  measure 
of  the  vital  force  which  is  in  our  reach.  A  heart-action 
which  maintains  its  uniformity,  and  is  but  little  dis- 
turbed by  the  various  exciting  causes,  indicates  a 
powerful  life  force  which  will  resist  all  ordinary  causes 
of  disease,  and  restore  health  under  circumstances  that, 
with  a  feeble  circulation,  would  be  hopeless. 

298.  Bleeding  from  Arteries  or  Teins.  —  Though 
the  heart  and  larger  arteries  are  well  secured  from 
injury  by  ordinary  accidents,  yet  the  superficial  vessels 
are  often  injured,  and  it  is  frequently  of  the  first  impor- 
tance to  be  able  to  distinguish  the  bleeding  of  an  artery 
from  that  of  a  vein,  as  this  discrimination  will  decide 
what  must  be  done.  (§  48.) 

When  an  artery  is  divided,  the  bleeding  can  be 
arrested  only  by  tying  the  vessel;  but  the  immediate 
danger  can  generally  be  met  by  compressing  the  vessel 
above  the  wound,  or  on  the  side  next  to  the  heart,  till 
a  surgeon  is  obtained. 

Recapitulation. 

The  circulatory  organs  are  in  sympathy  with  all  the  func- 
tions of  the  body.  Danger  from  compression  of  the  veins  by 
tight  clothing.  Nearly  all  the  activities  of  the  body  affect  the 
circulation  indirectly.  Temperature  and  circulation  mutually 
influence  each  other.  Reaction  from  exposure  to  cold  —  neces- 
sary precautions.  Mental  exercise  and  the  influence  of  the 
passions  affect  the  circulation. 


206  HYGIENE. 

LESSON    XXXVII. 

BREATHING. 

299.  Breathing  — -  its    complex    character.  —  The 

organs  concerned  in  respiration  are  intimately  con- 
nected with  a  long  train  of  dangers  to  health,  both 
from  the  defective  performance  of  their  functions,  and 
from  the  unwholesome  condition  of  the  air  used  in 
breathing.  Foremost  among  these  dangers  stand  prom- 
inent the  restrictions  on  the  respiratory  movements 
from  improper  dressing. 

We  have  already  described  (Lesson  VII)  the  process 
of  breathing  as  being  carried  on  jointly  by  the  dia- 
phragm, the  rnuscles  between  the  ribs  (intercostals), 
and  the  muscles  forming  the  front  part  of  the  abdomen. 
Now,  breathing  may  be  imperfectly  carried  on  by  the 
diaphragm  alone,  but  perfect  breathing  requires  the 
joint  action  of  all  these  organs,  operating  without 
restraint  and  with  the  utmost  freedom.  But  our 
modern  style  of  dress  defeats  this  end  so  completely, 
that  we  rarely  see  a  person  breathing  naturally. 

300.  Movement  of  the  Ribs  in  Breathing.  —  Much 
that  has  been  written  on  the  subject  of  tight  lacing  has 
been  misunderstood,   or  the   statements  have    been   so 
indefinitely  made  that  they  have  rather  served  to  mis- 
lead than  to  instruct  those  for  whose  benefit  they  were 
written. 

The  motion  of  the  ribs  in  expanding  the  chest  in- 
creases as  we  descend  in  the  series.  The  first  rib  is  a 
fixed  point,  and  the  second  one  is  moved  upward  a 
given  amount;  the  third  moves  twice  as  much  as  the 


BREATHING.  207 

second,  the  fourth  three  times  as  much,  and  so  on 
through  the  whole  series,  so  that  the  twelfth  rib  should 
have  eleven  times  as  much  motion  as  the  second  one. 
At  a  glance  it  will  be  seen  how  much  more  injurious 
it  is  to  compress  the  lower  than  the  upper  part  of  the 
chest,  yet  our  modern  styles  nearly  relieve  the  true 
ribs,  and  put  all  the  compression  on  the  false  and 
floating  ribs. 

301.  Injurious    effect    of  Compression.  —  But   the 

compression  of  the  chest  is  not  the  only  thing  to  be 
guarded  against  in  this  relation.  In  healthy  breathing 
there  is  a  free  motion  of  the  abdominal  muscles,  and 
if  this  motion  be  in  any  way  interfered  with,  the 
breathing  will  be  imperfect. 

To  suspend  the  lower  garments  by  a  band  passed 
around  the  loins,  will  prevent  all  free  motion  of  the 
muscles  on  the  front  and  sides  of  the  abdomen,  and 
to  that  extent  impede  respiration.  And  this  remark 
applies  not  merely  to  women's  clothing;  the  habits 
of  dress  common  among  men  confine  the  abdomen 
by  too  tight  a  waistband,  so  as  to  materially  interfere 
with  the  freedom  of  breathing.  The  lower  garments, 
whether  in  male  or  female  dress,  should  be  suspended 
from  the  shoulders,  so  as  to  leave  the  most  perfect 
freedom  of  motion  to  the  lower  part  of  the  chest  and 
abdomen.  Compression  need  not  be  violent  in  order 
to  be  injurious.  A  very  moderate  pressure,  constantly 
kept  up,  will  be  sufficient. 

302.  Compression  —  when    most    injurious.  —  Im- 
proper clothing  is  much  more  injurious  to  young  per- 
sons than  to  those  of  mature  age.     In  youth  the  car- 
tilages are  soft  and  yielding;  a  compression,  therefore, 

B.  P.— 18. 


208  HYGIENE. 

which  in  older  persons  would  hardly  be  felt,  will  in  a 
short  time  produce  permanent  distortion  of  the  ribs, 
and  entail  on  the  unfortunate  and,  perhaps,  unconscious 
subject  of  it,  a  feeble  vitality,  which  will  constantly 
invite  all  the  ailments  that  flesh  is  heir  to. 

Mothers,  in  the  dressing  of  their  children,  have  a 
great  responsibility  resting  on  them.  We  can  not  be 
too  often  reminded  that  vital  force  is  measured  by 
the  amount  of  chemical  change  going  on  in  the  body, 
and  that  these  changes  are  limited,  at  least  on  one  side, 
by  the  supply  of  oxygen  furnished  by  the  respiratory 
process.  Free  breathing  is  therefore  a  prime  condition 
of  vigorous  health. 

303.  Too  frequent  Breathing.  —  To  one  who  under- 
stands the  mechanism  of  breathing,  it  is  an  instructive 
lesson  to  watch  the  respiration  of  a  company  quietly 
seated  in  a  room.  Not  one  in  ten  breathes  correctly. 
Many  persons  breathe  with  the  diaphragm  alone; 
others  use  the  upper  part  of  the  chest  almost  exclu- 
sively; and  but  few  bring  into  requisition  all  the 
means  of  inflating  the  lungs. 

This  imperfect  filling  of  the  air-cells  compels  the 
breathing  to  be  more  frequent,  in  order  to  supply  in 
some  degree  the  deficiency  of  fullness.  But  this  in- 
creased frequency  not  only  exhausts  the  few  muscles  on 
which  the  whole  labor  is  imposed,  but  the  air  is  not  re- 
tained in  the  pulmonary  cells  long  enough  to  impart 
its  oxygen  fully  to  the  blood,  and  receive,  in  turn,  its 
charge  of  carbonic  acid  from  it.  A  healthy  person  with 
well-developed  lungs,  breathing  quietly,  will  fill  them 
about  fifteen  times  per  minute;  but  persons,  from  a 
bad  habit  of  breathing,  or  from  ill-developed  or  com- 


BREATHING.  209 

pressed  lungs,  frequently  respire  twenty  or  twenty-five 
times  per  minute. 

304.  Exercise    of  the    Tocal    apparatus. — A   free 
exercise  of  the  lungs  in  singing,  declaiming,  or  reading 
aloud,  with  careful  attention  to  the  method  of  breathing, 
is  the  best  means  of  correcting  vicious  habits  in  the 
use  of  the  lungs   and   their   associated  apparatus.     In 
these  exercises,  care  must  be  taken  that  the  diaphragm, 
ribs,  and  abdominal  muscles  are  all  brought  into  use 
and  act  in  concert. 

Many  public  speakers  and  singers,  when  they  suffer 
somewhat  from  embarrassment,  are  in  the  habit  of 
rigidly  contracting  the  abdominal  muscles,  and  holding 
them  firmly  in  that  attitude  during  the  whole  perform- 
ance. This  compels  more  frequent  breathing  than  is 
convenient,  deprives  the  voice  of  volume  and  force, 
and  gives  it  the  appearance  of  coming  from  the  upper 
part  of  the  throat  only.  Much  of  the  throat  disease  in 
public  speakers  may  be  traced  directly  to  this  vicious 
habit  of  breathing. 

305.  Imperfect     Breathing,     source     of     Feeble 
Health.  —  Imperfect   breathing,   from   whatever   cause 
it  may  arise,  is  more  to  be  dreaded  as  inducing  feeble 
health  than  almost  any  other  cause,  for  the  reason  that 
it  is  seldom  suspected  either  by  those  who  suffer  or  by 
their  friends.     Though  a  compressed  chest  and  unde- 
veloped lungs,  with  a  bad  habit  of  breathing,  may  not 
immediately  lead  to  any  actual  disease,  yet  the  dimin- 
ished   vital    force,    which    is    an    inevitable    result    of 
breathing  imperfectly,  will  greatly  impair  the  powrers 
of  endurance  —  the  ability  to  sustain  protracted  efforts 
either  of  muscle  or  mind. 


210  HYGIENE. 

With  this  diminished  vital  force  comes  the  enfeebled 
power  to  resist  the  encroachment  of  disease,  or  to  restore 
the  healthy  action  of  the  system  after  disease  has  super- 
vened. The  chances  of  recovery  from  sickness  are  al- 
ways augmented  by  a  well-developed  respiratory  ap- 
paratus and  a  good  habit  of  breathing.  Much  of  the 
feeble  health  that  is  complained  of  in  this  country, 
especially  among  women,  is  traceable  to  imperfect 
breathing  as  its  remote  cause. 

306.  Breathing   directly   connected    with    Life.— 

Eating,  drinking,  sleeping,  and  exercising  are  condi- 
tions of  life  and  health,  yet  they  are  only  remotely  so; 
but  breathing  is  an  immediate  and  indispensable  con- 
dition on  which  life  depends  directly;  it  is  therefore 
the  most  important  of  all  the  voluntary  functions  we 
perform.  Indeed,  respiration  is  so  immediately  con- 
nected with  life,  that  beyond  a  certain  point  of  volun- 
tary control,  the  Creator  has  wisely  removed  it  from 
our  personal  management,  and  placed  it  among  the 
involuntary  functions. 

In  this  view  of  its  importance,  it  is  surprising  to 
observe  how  little  attention  is  usually  paid  to  the 
whole  matter  of  respiration,  both  with  regard  to  how 
we  breathe  and  what  we  breathe.  Persons  are  often 
very  particular  to  have  their  food  scrupulously  clean, 
but  will  not  hesitate  to  breathe  the  air  of  a  crowded, 
ill-ventilated  hall,  or  to  inhale  volumes  of  second-hand 
tobacco  smoke. 

Recapitulation. 

Breathing  is  a  complex  function,  carried  on  by  the  joint 
action  of  several  organs.  Compression  of  the  lower  ribs  is  more 
injurious  than  that  of  the  upper  ones.  Bad  effects  of  com- 


PURE  AIR.  211 

pression  on  the  abdominal  muscles.  Tight  clothing  is  most 
injurious  to  the  young.  Too  frequent  breathing  defeats  the 
object  of  respiration.  Use  of  the  vocal  organs  as  a  means  of 
correcting  bad  habits  of  breathing.  Imperfect  breathing  is  a 
source  of  feeble  health. 


LESSON    XXXVIII. 

PURE   AIR. 

307.  Composition  of  the  Atmosphere.  —  A  healthy 
respiration  demands  that  pure  air  be  supplied  to  the 
lungs  at  appropriate  intervals  and  in  proper  quantities. 
This  question  of  pure  air  is  the  more  difficult  to  solve 
because  many  of  the  most  objectionable  impurities  give 
to  our  senses  no  evidence  of  their  presence.  The  atmos- 
phere consists  of  seventy-nine  parts  of  nitrogen  and 
twenty-one  parts  of  oxygen.  These  are  not  chemically 
combined,  but  in  a  state  of  intimate  mixture;  or, 
more  properly,  the  nitrogen  acts  as  a  solvent,  and 
the  oxygen  is  held  in  solution  in  it.  This  accounts 
for  its  uniformity  in  every  place  where  it  has  been 
examined. 

Besides  these  two  gases,  the  atmosphere  holds  a  vari- 
able quantity  of  watery  vapor,  carbonic  acid,  ammonia, 
and  other  volatile  substances,  which  it  receives  from  a 
thousand  sources.  These  impurities,  however,  where 
the  air  is  allowed  a  free  circulation,  seldom  exceed  one 
part  in  a  thousand.  It  is  only  where  the  air  is  confined 
that  they  accumulate  so  as  to  be  dangerous  to  those 
who  breathe  them. 


212  HYGIENE. 

308.  Natural  means  of  Purifying  the  Air.  — One 

of  the  most  beautiful  economies  in  nature  is  that  by 
which  the  air  is  purified  of  the  pollutions  that  are 
constantly  poured  into  it  from  the  breathing  of  ani- 
mals, the  burning  of  fires,  the  decomposition  of  vegeta- 
ble and  animal  matter,  etc.  Like  a  great  ocean,  the  air 
receives  from  all  these  sources  constant  streams  of  car- 
bonic acid  and  ammonia,  which,  if  there  were  no  coun- 
teracting agency,  would  soon  render  it  utterly  unfit  to 
be  breathed.  But  these  noxious  impurities  are  readily 
dissolved  in  water,  and  the  showers,  as  they  fall  from 
the  clouds,  wash  the  air  and  purify  it. 

To  assist  this  process,  the  vegetable  world  spreads  its 
broad,  leafy  surface  to  the  breeze,  where  myriads  of 
mouths  on  every  leaf  are  open  to  drink  up  the  carbonic 
acid  from  the  air,  and  appropriate  it  to  their  own  use. 
In  this  same  leaf  the  impurity  is  decomposed,  and  its 
oxygen  returned  to  the  air  to  supply  the  constant  waste 
of  it  by  animals. 

309.  Sources  of  Impure   Air.  —  The   influence   of 
growing  vegetation  in  purifying  the  air  suggests   the 
importance  of  trees  and  shrubbery  about  our  dwellings, 
and  of  lawns  and  parks  in  the  vicinity  of  large  cities, 
where  they  will  serve  as  reservoirs  of  pure  air.     What 
we  are  able  to  do,  locally,  to  purify  the  air  for  our  use, 
may  be  but  a  small  matter,  but  much  may  be  gained 
for  health  by  carefully  shunning  the  sources  of  impure 
air.     Ponds  of  stagnant  water,  marshes,  and  other  accu- 
mulations of  decomposing  vegetable  and  animal  matter, 
should  be  studiously  avoided. 

Large  assemblies  in  imperfectly  ventilated  rooms  are 
most  fruitful  sources  of  mischief  to  the  health  of  those 


PUKE  AIR.  213 

who  visit  them.  Air  that  has  been  once  breathed  is 
unfit  for  use  until  it  has  mingled  with  the  great  atmos- 
pheric ocean,  and  its  original  composition  has  been 
restored.  By  a  wise  provision,  to  prevent  re-inhaling 
our  own  breath,  it  is  rarefied  by  heat,  and  caused 
to  rise  above  our  heads  as  soon  as  exhaled  from  the 
lungs. 

310.  Oxygen  —  its  diminution  by  Breathing.  —  It 

has  been  ascertained  by  careful  experiment  that  air 
exhaled  from  healthy  lungs  has  lost  about  one-fourth 
of  the  oxygen  it  originally  contained,  and  that  the 
volume  has  been  maintained  by  the  substitution  of 
carbonic  acid  for  the  oxygen  abstracted.  Some  might 
infer  from  this  that  breathing  the  same  air  four  times 
would  rob  it  of  all  its  oxygen.  This  is  not  the  case. 
Air  that  has  lost  one-fourth  of  its  oxygen  by  a  first 
inhalation,  will  lose  less  than  one-eighth  the  second 
time  if  is  inhaled;  and  when  the  oxygen  has  been 
diminished  one-half  the  original  quantity,  the  air  will 
no  longer  support  life. 

On  the  other  hand,  the  capacity  of  air  to  dissolve 
carbonic  acid  diminishes  in  a  rapid  ratio  by  the  amount 
dissolved.  Now,  when  we  bear  in  mind  that  breathing 
performs  the  double  function  of  supplying  oxygen  to 
the  blood  and  removing  carbonic  acid  from  it,  we  shall 
perceive  the  importance  of  having  the  first  use  of  all 
the  air  we  breathe. 

311.  Importance   of  thorough   Ventilation.  —  The 

proper  ventilation  of  rooms  is  a  subject  involving  more 
of  health  and  comfort  than  has  been  generally  appre- 
hended. Public  halls,  churches,  school-rooms,  private 
apartments,  and  especially  sleeping-rooms,  should  at  all 


214  HYGIENE. 

times  have  a  free  supply  of  pure,  fresh  air,  and  a  con- 
stant removal  of  that  which  has  been  vitiated  by 
breathing. 

It  is  not  necessary  that  air  should  be  cold  in  order 
to  be  pure.  Air  may  be  warmed  to  any  desirable 
temperature  by  a  proper  apparatus,  and  yet  retain  its 
healthy  proportions  unchanged.  The  only  advantage 
in  breathing  cold  air  is,  that  heat  expands  air  largely, 
and  consequently  a  given  volume  of  cold  air  contains 
more  oxygen  than  the  same  volume  of  heated  air.  In 
warming  apartments  by  a  supply  of  heated  air,  we 
must  guard  against  passing  the  air  over  red-hot  surfaces 
of  iron,  as  a  portion  of  its  oxygen  will  combine  with 
the  iron,  and  thus  the  amount  available  for  breathing 
will  be  diminished  in  the  same  proportion. 

312.  Care  necessary  in  Warming  Rooms.  —  When 
stoves  or  furnaces  are  used  for  the  purpose  of*heating 
apartments,  great  care  must  be  taken  that  the  gases 
resulting  from  combustion  of  the  fuel  do  not  escape 
into  the  air  being  warmed  by  it.  Dr.  Nichols,  of 
Boston,  has  demonstrated,  by  a  series  of  careful  experi- 
ments, that  cast-iron,  when  highly  heated,  will  permit 
carbonic  oxide  to  pass  through  its  pores,  and  render 
the  air  thus  heated  unsafe. 

An  open  grate  or  wood  fire  with  a  strong  dr^ft, 
though  not  a  very  good  method  of  economizing  heat, 
is  an  excellent  ventilator  and  a  safe  way  of  warming 
small  rooms;  but  when  large  halls  or  suites  of  rooms 
require  heating,  currents  of  warm  air  should  be  con- 
stantly introduced,  which  will  demand  that  means  be 
provided  for  the  discharge  of  a  corresponding  current 
of  vitiated  air.  This  warm  air  should  be  supplied 


PURE  AIR.  215 

either  from  a  wrou  grit-iron  furnace  or  from  a  chamber 
heated  by  coils  of  steam  or  hot  water  pipes. 

313.  Bad  effects  of  ill-ventilated  School-rooms.— 

In  large  manufacturing  establishments,  where  un- 
healthy gases  are  generated,  provisions  should  be  made 
for  carrying  these  away,  by  means  of  a  high  venti- 
lating stack,  in  which  a  rapid  current  is  made  to 
ascend  constantly  by  the  aid  of  proper  machinery, 
thus  effecting  a  thorough  renovation  of  the  air. 

The  imperfect  ventilation  of  school-rooms  is  an  evil 
whose  consequences  can  hardly  be  measured;  and  they 
are  the  more  to  be  dreaded  because  their  effects  are  of 
such  a  character  as  seldom  to  occasion  immediate  alarm. 
The  direct  consequence  of  breathing  air  containing 
a  mixture  of  carbonic  acid  below  the  point  producing 
a  sense  of  suffocation,  is  to  oppress  the  brain  with  a 
feeling  of  languor  and  dullness,  followed  by  an  almost 
irresistible  tendency  to  sleep.  In  this  condition  neither 
teachers  nor  pupils  are  fit  for  duty.  In  a  room  twenty- 
five  feet  square,  fifty  pupils  will  breathe  all  the  air  it 
contains  in  a  little  more  than  two  hours.  After  the 
first  hour,  the  time  spent  in  such  a  school-room  is  worse 
than  wasted. 

3U.  Alcohol  and  Tobacco— influence  on  Respira- 
tion.—  It  is  important,  in  the  relation  of  acquiring  and 
maintaining  vigorous  health,  that  the  lungs  be  pre- 
served in  such  a  state  that  the  air  will  freely  enter  the 
whole  of  each  lung,  and  that  the  air-cells  be  in  such  a 
condition  that  the  oxygen  from  the  air,  and  the  car- 
bonic acid  and  watery  vapor  from  the  blood,  may  be 
freely  transmitted  through  the  walls  of  the  cells. 

It  is  a  familiar  fact,  that  when  spirituous  liquors  are 
B.  P.— 19. 


216  HYGIENE. 

taken  into  the  stomach,  the  alcohol  begins  directly  to 
pass  oft*  by  the  lungs,  and  may  be  detected  in  the 
breath.  But  so  delicate  a  membrane  as  that  of  the 
air-cells  can  not  be  subjected  to  the  action  of  alcohol 
without  serious  injury.  The  same  may  be  said  of  in- 
haling an  atmosphere  foul  with  tobacco  smoke.  The 
narcotic  effect  of  tobacco  smoke  in  its  second  use  is 
worse  than  the  first  use  of  the  fumes,  as  in  that  in- 
stance the  poison  is  carried  to  the  lungs,  instead  of 
merely  affecting  the  mucous  membrane  of  the  mouth. 

Recapitulation. 

Healthy  respiration  requires  pure  air  in  proper  quantities. 
Decaying  animal  and  vegetable  matters  vitiate  the  air.  Rain 
and  growing  vegetation  are  means  of  purifying  the  air.  Large 
assemblies  corrupt  it.  Air  once  breathed  is  unfit  for  use  till  it 
is  purified.  In  exhaled  air,  the  oxygen  is  reduced  and  car- 
bonic acid  increased.  Ill  ventilation  affects  brain  functions. 
Narcotics  diminish  the  quantity  of  oxygen  retained  from  the 
air  inhaled. 


LESSON    XXXIX. 

ANIMAL   HEAT. 

315.  Uniform  Temperature  of  the  Body. — Animal 
heat,  being  so  intimately  connected  with  the  respira- 
tory function,  will  be  appropriately  considered  in  this 
place.  The  temperature  of  a  healthy  adult  is  about 
ninety-eight  degrees;  in  infancy  it  is  a  little  greater, 
and  in  old  age  somewhat  less.  It  is  astonishing  to 
observe  with  what  regularity  the  general  temperature 


ANIMAL  HEAT.  217 

^s  maintained  in  all  climates,  and  under  extreme  vicis- 
situdes of  season.  When  persons  are  exposed  in  ex- 
tremely cold  weather,  the*  temperature  of  the  extremi- 
ties and  of  the  exposed  parts  of  the  face  often  sinks  to 
near  the  freezing  point:  but,  even  at  this  time,  a 
delicate  thermometer,  placed  in  the  arm-pit  or  under 
the  tongue,  will  show  little  or  no  variation  from  the 
uniform  standard  of  ninety-eight  degrees. 

Dr.  Kane,  in  his  Arctic  explorations,  was  often  ex- 
posed for  hours  to  a  temperature  between  sixty  and 
seventy  degrees  below  zero,  without  materially  affecting 
the  heat  of  his  body ;  and  in  a  number  of  well-authen- 
ticated cases,  persons  have  subjected  themselves  for 
hours  to  a  temperature  above  the  boiling  point  of 
water,  and  still  the  thermometer  under  the  tongue 
marked  ninety-eight  degrees. 

316.  Evaporation  and  Temperature. — These  aston- 
ishing results  can  be  explained  only  by  understanding 
the  relations  existing  between  the  pulmonary  and 
cutaneous  surfaces  of  the  body.  If  the  proper  amount 
and  kind  of  food  be  taken  and  digested,  the  tempera- 
ture will  be  measured  by  the  quantity  of  oxygen  re- 
ceived through  the  lungs  in  respiration;  but  the 
evaporation  of  water  is  a  cooling  process,  and  reduces 
temperature  in  proportion  to  its  rapidity. 

The  rapidity  of  evaporation  depends,  to  a  very  great 
extent,  on  the  temperature  of  the  air.  In  a  low  tem- 
perature, the  evaporation  from  the  surface  of  the  body 
is  virtually  suspended,  and  the  heat  evolved  in  the 
system  is  retained  only  as  it  is  conducted  away  by 
exposure  of  the  surface  to  the  cold  air.  When  the  body 
is  exposed  to  the  other  extreme  of  temperature,  the 


218  HYGIENE. 

evaporation  of  perspiration  from  the  surface  is  suffi- 
cient to  keep  the  temperature  down  to  ninety-eight 
degrees. 

317.  Conditions  of  a  uniform  Temperature.  —  The 

power  to  maintain  this  constant  equilibrium  of  tem- 
perature depends  directly  on  the  healthy  action  of  the 
pulmonary  surface — that  is,  the  inner  surface  of  the  air- 
cells;  and  on  the  external,  or  perspiratory  surface  —  the 
skin;  and  indirectly,  on  the  supply  of  oily,  starchy,  or 
saccharine  food,  and  the  perfect  digestion  of  the  same. 
The  failure  of  either  of  these  conditions  will  be  followed 
by  a  corresponding  disturbance  in  the  power  to  main- 
tain an  equal  temperature  under  changes  in  the  heat 
of  the  atmosphere. 

In  cold  weather,  the  first  condition  of  security 
against  suffering  is  full  and  free  breathing  of  pure 
air  into  healthy  lungs.  Many  persons,  on  leaving  a 
warm  room  and  going  into  a  cold  atmosphere,  feel  a 
sense  of  chilliness,  which  induces  a  short,  shallow 
breathing,  as  though  they  feared  to  fill  the  lungs 
with  cold  air.  A  few  full  inspirations  will  relieve 
this  chilly  sensation  and  restore  a  feeling  of  comfort- 
able heat. 

318.  Precautions  against  a  Cold  Atmosphere. — But 

if  there  is  an  inability  to  fill  the  lungs,  whether  from 
temporary  disturbance  or  from  permanent  disease,  care 
must  be  observed  in  making  sudden  transitions  from  a 
warm  to  a  cold  atmosphere.  Persons  who  have  natu- 
rally small  lungs,  or  who  dress  so  that  the  larger  part 
of  the  pulmonary  surface  is  rendered  useless,  or  those 
who,  from  present  or  previous  disease,  have  the  full 
use  of  only  a  small  part  of  the  breathing  apparatus, 


ANIMAL  HEAT.  219 

generate  heat  "feebly,  and  should  not  be  exposed  to 
low  temperatures.  But  even  if  the  lungs  supply  a 
full  amount  of  oxygen,  the  stomach  may  not  have 
furnished  the  supply  of  combustible  material  with 
which  this  is  to  unite;  there  will  then  be  a  corre- 
sponding inability  to  maintain  the  temperature  on 
exposure  to  cold. 

319.  Overheated   Rooms — ill    effects.  —  Dyspeptics, 
and   those  who   are   suffering  from  pulmonary  disease, 
or  have  a  predisposition   to   it,  while   they  are   careful 
to  avoid  sudden  transitions  from  one  extreme  of  tem- 
perature to  another,  should  be  equally  careful  to  guard 
against  the  too  common  error  of  constantly  living   in 
overheated   rooms. 

Let  invalids  remember  that  the  chemical  action  which 
goes  on  between  the  air  we  breathe  and  the  food  we 
digest  is  not  only  the  source  of  animal  heat,  but  of 
vital  force.  That  uncomprehended,  and  perhaps  incom- 
prehensible power  also,  by  which  all  the  movements  of 
the  living  machinery  are  performed,  is  more  or  less 
directly  connected  with  the  same  chemical  changes; 
and  whatever  diminishes  the  amount  of  these  changes, 
impairs  the  life-force  in  the  same  ratio.  In  a  room 
heated  to  near  the  natural  temperature  of  the  body, 
there  is  but  little  demand  for  food,  because  there  is 
very  little  chemical  change  required  to  supply  the 
small  deficiency  of  heat;  but  the  vital  force  is  also 
Diminished  in  like  proportion. 

320.  Proper  Temperature  of  Rooms. — This  accounts 
for  the  relaxing   effect  of  external  heat  —  the  languor 
and  lassitude  of  those  who  spend  their  days  and  nights 
in  heated  apartments.     This  effect  is  often  heightened 


220  HYGIENE. 

i 

by  imperfect  ventilation,  suffering  the  air  to  become 
loaded  with  carbonic  acid  and  other  impurities.  The 
stomach  seldom  digests  food  when  there  is  no  demand 
for  it  in  the  system ;  and  if  food  be  taken  under  these 
circumstances,  indigestion  must  follow. 

Living-rooms,  school-rooms,  offices,  etc.,  should  be 
maintained  as  nearly  as  possible  at  a  temperature  be- 
tween sixty  and  sixty-five  degrees.  This  will  leave 
some  thirty-five  degrees  of  temperature  to  be  supplied 
by  the  vital  apparatus,  and  that  will  insure,  as  a  con- 
sequent, sufficient  force  to  give  energy  and  efficiency 
to  the  life-functions.  Sleeping  apartments  may  safely 
have  a  lower  temperature  —  say  fifty  degrees. 

321.  Means  of  reducing  Heat.— In  the  artificial  heat 
produced  by  the  burning  of  fuel,  we  have  a  means  of 
guarding  against  low  temperature,  that  may  be  made 
available  in  all  in-door  occupations;  and  proper  cloth- 
ing, exercise,  breathing,  and  food  will  render  out-door 
employments  comparatively  comfortable  in  any  ordi- 
nary temperature.  But  the  other  extreme,  the  high 
temperature  of  summer,  is  not  so  readily  controlled; 
much  may  be  done,  however,  in  this  direction  that 
has  hardly  been  attempted  yet. 

Buildings  with  thick  walls,  or  with  an  air-chamber 
between  the  outer  and  inner  surface,  will  maintain  a 
much  more  uniform  temperature  than  can  be  secured 
by  the  walls  in  common  use.  The  evaporation  of  water 
is  the  method  employed  in  nature  to  mitigate  extreme 
heat  every-where.  The  three  great  oceans  which  stretch 
across  the  tropics  present  a  broad  evaporating  surface, 
which  serves  to  cool  the  trade-winds  that  sweep  over 
the  continents.  If  the  entire  surface  of  the  .globe 


ANIMAL   HEAT.  221 

within    the    tropics    were    land,    neither    animal    nor 
vegetable   life   could  be  sustained  on  it. 

322,  Exposure  to  currents  of  Air.  —  Evaporation 
may  be  made  available,  to  some  extent  at  least,  to  cool 
down  the  intensity  of  summer  heat  in  and  around  our 
dwellings.  While  our  clothing  should  allow  the  air  to 
penetrate  freely,  that  the  perspiration  may  evaporate 
easily  from  the  surface  of  the  body,  yet  care  must  be 
taken  lest  currents  of  dry  air  produce  such  rapid  evap- 
oration as  to  arrest  or  obstruct  the  perspiration  by  a 
sudden  reduction  of  the  temperature. 

It  is  always  safer  to  have  the  evaporation  take  place 
from  the  surface  of  our  clothing  rather  than  directly 
from  the  skin.  The  influence  of  even  a  rapid  breeze, 
when  we  are  perspiring  freely,  may  be  borne  with 
little  danger  if  we  continue  in  active  exercise;  but 
when  the  exercise  is  suspended,  currents  of  air  should 
be  avoided,  and  additional  clothing  should  be  put  on. 

Recapitulation. 

Temperature  of  the  healthy  body  is  uniform.  Evaporation  is 
a  regulator  of  temperature.  Proper  breathing,  appropriate  food, 
and  a  healthy  condition  of  the  skin  are  necessary  to  a  uniform 
heat.  Precautions  should  be  taken  against  a  cold  atmosphere 
by  those  who  have  weak  or  diseased  lungs.  Overheated  rooms 
are  to  be  guarded  against.  Proper  temperature  of  living-rooms 
is  between  sixty  and  sixty-five  degrees  Fahrenheit.  Evapora- 
tion is  the  natural  means  of  reducing  temperature.  When 
heated,  avoid  currents  of  air. 


222  HYGIENE. 


LESSON    XL. 

BATHING  —  CLOTHING. 

323.  Bathing   necessary.  —  In  order  to  maintain  a 
uniform  temperature   of   the  body,   the   skin   must   be 
kept  in  a  healthy  condition,  so  that  when  the  heat  of 
the  body  rises  above  ninety-eight  degrees,  perspiration 
will    be    increased,    and    evaporation    will    reduce    the 
temperature  to  the  healthy  standard;  or,  on  the  other 
hand,  if  the  heat  of  the  body  falls  below  that  standard, 
the   action  of  the   skin   will   be   proportionally  dimin- 
ished,  and  the   animal   heat    thus    preserved.     But    in 
order  that  the   skin   may   thus  act  as  a   regulator   of 
animal  heat,  it  must  be  kept  clean.     It  is  one  of  the 
channels    through    which   the    waste    material    of   the 
body  is  carried  away. 

When  the  perspiration  evaporates,  it  leaves  on  the 
surface  of  the  skin  the  saline  and  animal  matter  which 
it  held  in  solution.  But  the  skin  secretes  oil,  also;  and 
this,  with  the  residuum  from  the  evaporation  and  the 
natural  waste  from  the  surface  of  the  cuticle,  forms  a 
gummy  substance  which  is  liable  to  obstruct  greatly 
the  natural  outlets  through  the  skin. 

324.  How  to  Bathe. — To  remove  this  accumulation, 
as  well   as   that  which    is   added   to   it   from  external 
sources,  the  whole   surface  of  the   body  should  be   fre- 
quently and  carefully  washed.     Bathing,  as  a  means  of 
cleansing  the  skin,  should  be   resorted   to,  during  the 
warm  seasons,  at  least  as  often  as  twice  a  week.     The 
bath  should  be  of  soft  water,  and  the  temperature  be- 
tween ninety  and  one   hundred  and   ten   degrees.     In 


BATHING  —  CLOTHING.  223 

order  to  dissolve  the  oily  accumulations  more  certainly, 
fine  soap  should  be  used  moderately,  and  the  surface 
briskly  rubbed  with  a  soft  sponge,  and  dried  with  a 
coarse  towel. 

Care  must  be  observed  in  the  use  of  strong  potash 
soap,  in  bathing,  lest  the  oil  should  be  so  completely 
removed  from  the  cuticje  that  its  surface  will  be  ex- 
posed to  the  air,  and  become  dry  and  chapped  from  its 
action.  If  soft,  warm  water  be  used,  nothing  but  the 
mildest  soaps  will  be  necessary  to  cleanse  the  skin 
effectually. 

325.  Bathing  for  other  Purposes. — Bathing  may  be 
resorted  to  for  other  purposes  than  that  of  cleansing  the 
skin.  Where  the  cutaneous  circulation  is  feeble,  and 
the  temperature  of  the  surface  habitually  too  low,  a 
hot  bath  may  be  taken  for  the  purpose  of  inviting  the 
circulation  to  the  surface.  For  this  purpose  the  tem- 
perature of  the  bath  may  range  between  one  hundred 
and  twenty  and  one  hundred  and  thirty  degrees.  Those 
who  resort  to  the  use  of  the  hot  bath  must  be  careful 
not  to  suffer  its  use  to  grow  into  a  habit. 

What  we  have  already  said  (Lesson  XXXIX)  on  the 
subject  of  overheated  rooms,  applies  equally  to  any 
other  habitual  substitution  of  external  heat  for  that 
which  is  produced  by  the  chemical  changes  going  on 
in  the  living  body.  If  the  vital  force  be  not  very 
feeble,  the  circulation  may  be  attracted  to  the  surface 
as  certainly  and  more  permanently  by  a  cold  bath  — 
or,  rather,  by  the  reaction  which  follows  a  cold  bath  — 
than  by  the  direct  application  of  heat.  To  secure  this 
object,  the  bath  should  have  a  temperature  of  about 
seventy  degrees,  and  should  not  be  continued  more 


224  HYGIENE. 

than  two  or  three  minutes,  being  followed  by  brisk 
friction  on  the  surface  with  a  coarse  towel  or  hair- 
cloth. 

326.  The    Plunge-bath    and    Shower-bath.  —  The 

bath  may  be  used  for  the  purpose  of  rousing  up  the 
sluggish  action  and  torpid  sensibilities  of  the  body. 
To  accomplish  this  end,  the*  whole  body  should  be 
plunged  at  once  into  water  of  a  temperature  between 
sixty  and  seventy  degrees,  and  immediately  wiped  dry, 
and  wrapped  in  a  soft  blanket  or  clothed  in  flannel. 
The  same  purpose  can  be  accomplished  as  effectually 
and  sometimes  more  conveniently  by  a  shower-bath. 
But  in  the  use  of  both  the  plunge  and  shower-bath 
we  must  be  careful  not  to  mistake  an  exhausted  vitality 
for  a  merely  torpid  condition  of  the  system. 

In  general  it  will  be  safer  to  begin  either  the  plunge 
or  shower-bath  with  a  temperature  of  eighty  degrees, 
and  if  the  bath  is  followed  by  a  glow  of  heat  on  the 
surface,  we  may  safely  venture  to  reduce  the  tempera- 
ture; but  if  not,  we  should  at  once  desist.  Medicated 
and  vapor-baths  are  frequently  used,  but,  being  reme- 
dial agents,  they  do  not  belong  to  the  subject  of 
hygiene. 

327.  Clothing,   as   related    to    health.  — To   enable 
the  skin  to   perform  its  office  in  such  a  manner  as  to 
regulate  effectually  the  temperature  of  the   body,  care- 
ful attention  must  be  paid  to  the  subject  of  clothing. 
This   embraces  both   the   material   used  in   the   fabrics 
worn,  and  the  adjustment  of  it  to  the  body. 

So  far  as  the  subject  is  related  to  health,  the  prime 
object  of  clothing  is  to  protect  the  surface  of  the  body 
from  vicissitudes  of  temperature,  by  interposing  between 


BATHING  —  CLOTHING.  225 

it  and  the  external  air  a  non-conducting  substance, 
which  will  transmit  the  heat  of  the  body  but"  slowly 
when  the  air  is  colder  than  blood-heat,  and  which 
will  arrest  the  scorching  heat  of  the  sun,  when  his  rays 
have  a  temperature  above  the  natural  heat  of  the  body. 
Substances  differ  widely  in  their  conducting  properties; 
but  in  the  fabrics  used  far  clothing,  the  chief  difference 
consists  in  the  porous  texture  of  the  cloth,  or  the 
amount  of  air  in  the  fabric. 

328.  Qualities    of    Good    Clothing.  —  Wool,    when 
carded   and   spun    in  the  ordinary  manner,   forms   an 
elastic,  soft,   and  porous   texture,   and    is   therefore   an 
excellent   non-conductor  of  heat;    but   the  same   wool, 
if  combed  so  that  the  fibers  will  lie  parallel,  will  form 
a  firm,  hard,  worsted  thread,  which,  when  woven,  will 
be  almost  as  good  a  conductor  as  linen.     Cotton  spun 
with  a  slack  twist,  and  softly  woven,  will  conduct  heat 
but  little  better  than  flannel;   but  ii  hard  twisted  and 
firmly  woven,  cotton  goods  conduct  heat  freely. 

Another  important  property  of  a  good  material  for 
clothing  is,  that  it  shall  not  absorb  and  retain  moisture 
to  any  considerable  extent.  A  good  clothing  material, 
while  it  will  not  permit  a  current  of  air  to  pass 
through  it  directly,  yet  it  must  be  so  porous  as  to 
transmit  the  insensible  perspiration  without  obstruc- 
tion. 

329.  Variations   of  Clothing.  — Clothing  should  be 
varied  with  the  climate  and  season,  but  this  variation 
should  have  regard  more  to  quantity  than  quality  of 
clothing.     In  hot  climates,  and  in  warm  weather  in  all 
climates,  fewer  garments  should  be  worn,  and  those  of 
lighter  fabrics;   but  still  a  non-conductor  is  needed,  to 


226  HYGIENE. 

prevent  the  injurious  effects  of  sudden  changes  of  tem- 
perature, from  currents  of  air,  or  transitions  from  sun- 
shine to  shade.  The  direct  rays  of  the  sun  in  the 
summer  months  frequently  give  a  temperature  far 
above  blood-heat,  and  persons  exposed  to  this  require 
the  protection  of  the  best  non-conductors  they  can 
command. 

The  materials  of  clothing  in  common  use  are  fur, 
wool,  silk,  cotton,  and  linen;  and  their  value  as  cloth- 
ing material  is  in  the  order  they  occupy  in  this  list. 
For  protection  against  intense  cold,  fur  is  the  best  dress 
material  known.  Its  high  price  and  the  difficulty  with 
which  it  is  cleansed  are  the  principal  objections  to  its 
general  use  as  winter  clothing. 

330.  Wool,  Silk,  Cotton,  and  Linen.  —  Fine  wool, 
made  into  loose,  soft  fabrics,  is  the  best  substitute  for 
fur,  and,  indeed,  meets  all  the  demands  of  comfort, 
health,  and  beauty  in  dress  material.  Silk  is  a  good 
non-conductor  of  heat,  and  absorbs  very  little  moisture, 
but  its  high  price  has  hitherto  prevented  its  general 
use  in  dress.  Cotton  has  a  wide  range  in  its  conduct- 
ing properties,  depending  on  the  mode  of  its  manu- 
facture. Cotton  flannels  are  nearly  equal  to  woolen 
fabrics  as  non  conductors,  while  the  hard-twisted, 
closely-woven  shirtings  differ  but  little  from  linens 
in  this  respect. 

From  the  round,  hard  character  of  the  fiber,  flax  and 
hemp,  in  all  the  forms  of  their  manufacture,  are  good 
conductors  of  heat,  and  consequently  the  worst  material 
for  clothing  in  use.  White  linen,  worn  as  an  outer 
garment,  is  a  good  reflector  of  sunshine.  This,  to  some 
extent,  counteracts  its  defect  as  a  conductor.  Under- 


HYGIENE  OF  BONES.  227 

clothing  should  be  changed  frequently  and  kept  scrupu- 
lously clean. 

Recapitulation. 

A  healthy  action  of  the  skin  is  important  in  maintaining  a 
uniform  temperature.  To  secure  this,  frequent  bathing  is  neces- 
sary. Bathing  may  be  used  as  a  means  of  influencing  the 
circulation  of  the  blood.  Caution  in  the  use  of  warm  baths. 
Rules  for  using  the  plunge-bath  and  shower-bath. 

Clothing  is  directly  related  to  health.  A  good  clothing  mate- 
rial must  be  an  imperfect  conductor  of  heat.  Mode  of  manu- 
facture has  much  to  do  with  the  conducting  property  of  cloth- 
ing materials. 


LESSON    XLI. 

HYGIENE   OF   BONES. 

331.  Bone  Nutrition  —  its  demands. — The  apparatus 
of  voluntary  motion  is  much  less  complicated  than  that 
of  either  of  the  other  systems,  and  consequently  less 
liable  to  derangements  and  disturbances  of  its  functions. 
The  osseous  or  bony  frame-work  of  the  body,  for  its 
proper  development  and  the  maintenance  of  its  healthy 
action,  demands  attention  to  food,  exercise,  and  security 
from  external  injuries. 

The  food  necessary  to  supply  the  material  for  the 
formation  and  repair  of  bone,  consists  of  those  articles 
which  are  rich  in  phosphate  of  lime,  such  as  fish  and 
other  forms  of  animal  flesh,  eggs,  wheat  bread,  etc. 
Many  vegetables  and  fruits,  which  are  otherwise  very 


228  HYGIENE. 

nutritious,  are  nearly  destitute  of  bone-earth,  and  per- 
sons living  on  these  exclusively  can  not  develop  and 
maintain  a  healthy  bony  system.  Potatoes,  for  example, 
while  they  are  rich  in  the  starchy  elements  of  food,  and 
contain  a  fair  proportion  of  the  nitrogenous  or  muscle- 
forming  material,  are  deficient  in  bone-earth;  and  the 
bones  of  persons  living  exclusively  on  such  diet  become 
soft  and  often  distorted. 

332.  Oversupply  of  Bone-earth  —  its  effects.  —  Per- 
sons who  are  very  fond  of  what  they  please  to  call  good 
living  —  that  is,  a  diet  rich  in  animal  food  —  frequently 
suffer  from   ari   oversupply  of   bone-earth.     The   bones 
become    hard   and    brittle,    and    even    slight   accidents 
result   in  fractured  bones,  often   seriously  endangering 
life.     This  redundancy  of  phosphates  in  the  food  may 
give  rise  to  gouty  concretions  about  the  joints,  resulting 
in  a  disease  alike  troublesome,  painful,  and  difficult  to 
cure. 

These  two  conditions  frequently  mark  the  opposite 
extremes  of  society.  Rickets  and  other  bony  deformi- 
ties indicate  the  poor  diet  of  the  children  of  want, 
while  fractured  bones  from  slight  accidents,  and  gouty 
ailments,  are  the  results  of  affluence  and  ease.  The 
remedy  for  both  lies  in  a  rational  diet  and  proper 
exercise. 

333.  Distortion  of  Bones — how  produced.  —  Both 
the  size  and  strength  of  the  bones  composing  the  frame 
of  the  body  will  depend  much  on  the  judicious  use  of 
them.     Like  every  other  organ  of  the  body,  the  bones 
during  the   period  of  growth  require  regular  exercise, 
in  order  to  their  full  development  both  in  regard  to 
their  perfect  organization  and  their  proper  size.     But  at 


HYGIENE  OF  BONES.  229 

this  period  all  occupations  which  require  a  constrained 
or  unnatural  attitude  of  the  body,  or  which  demand 
hours  to  be  spent  in  the  standing  position,  should  be 
carefully  avoided. 

The  bones  of  growing  persons  are  quite  soft  and 
flexible,  and  will  yield  to  a  constant  pressure;  and 
if  that  force  be  applied  in  an  unnatural  direction,  the 
bones  will  be  permanently  curved,  and  the  body  mis- 
shapen and  deformed.  Scholars  at  their  desks  should 
be  required  to  sit  upright,  so  that  the  weight  may  be 
supported  vertically  on  the  spinal  column. 

334:.  Freedom  of  Motion  necessary.  —  Persons  fol- 
lowing sedentary  employments  should  so  arrange  their 
work  that  they  will  not  be  required  to  assume  a  stoop- 
ing attitude.  With  all  persons,  such  positions  of  the 
body  are  injurious  to  health,  but,  to  the  young,  perma- 
nent deformity  is  almost  certain  to  be  added  to  the 
present  injury.  This  mischief  results  not  so  much 
from  assuming  improper  attitudes  as  from  the  con- 
tinuance of  them.  Children  at  natural,  healthful  play 
throw  the  body  and  limbs  into  almost  every  conceiv- 
able position,  but  they  change  their  attitudes  every 
moment,  and  no  harm  result?. 

In  childhood,  the  symmetrical  development  of  the 
bony  skeleton  requires  perfect  freedom  of  motion,  and 
such  active  employments  or  plays  as  will  give  a  great 
variety  of  motions  to  the  body,  and  a  constant  change 
of  position.  The  perfect  play  of  all  the  organs  in 
mature  life  demands,  as  a  first  condition,  that  there 
be  no  malformation  of  the  bones  by  careless  or  improper 
treatment  in  youth. 

335.  Compression   from   Clothing.  —  The    clothing 


230  HYGIENE. 

of  young  persons  should  be  adjusted  with  special  refer- 
ence to  the  fact  that,  while  the  bones  are  yet  flexible 
from  the  large  proportion  of  animal  matter  they  con- 
tain, even  a  very  gentle  pressure,  continued  from  day 
to  day,  will  curve  and  distort  the  bones,  and  thus 
produce  permanent  malformation. 

In  this  manner  the  Chinese  practically  render  their 
women  cripples  for  life ;  and  a  tribe  of  savages  in  the 
Rocky  Mountains,  by  a  similar  process,  deform  the 
head  in  childhood  so  as  to  produce  a  nation  of  mon- 
strosities; and  thousands  of  children  in  this  country, 
by  a  very  moderate  pressure  on  the  floating  ribs, 
continued  through  the  growing  period,  have  the  chest 
so  narrowed  at  the  base  as  practically  to  diminish 
the  breathing  power  at  least  one-half,  and,  as  a  con- 
sequence, reduce  the  force  of  all  the  vital  functions  in 
the  same  ratio. 

336.  Deformed  Feet  —  how  produced.  —  Multitudes 
thus  deformed  in  infancy  drag  out  a  miserable  life, 
under  the  false  impression,  that  their  daily  suffering 
from  feeble  health  is  a  mysterious  visitation  of  Divine 
Providence.  In  childhood  and  youth,  the  dress  of  either 
sex  should  be  so  loose  as  to  admit  of  the  fullest  inflation 
of  the  lungs  without  obstruction  or  constraint. 

In  dressing  the  feet  there  is  great  liability  to  distort 
the  bones  of  the  toes  and  the  metatarsal  bones.  But 
few  feet  can  be  found  in  this  country  which  retain  the 
natural  form  of  the  human  foot,  as  seen  in  the  statuary 
of  the  Greeks.  Though  this  is  a  minor  evil  compared 
with  the  deformity  of  the  chest,  yet  activity  and  grace- 
fulness of  movement  is  greatly  impaired  by  every  de- 
parture from  the  natural  form  of  the  foot,  and  the 


HYGIENE  OF  BONES.  231 

ability   to- -participate    in    that   most   healthful   of  all 
forms  of  exercise,  walking,  is  proportionally  reduced. 

337.  Spinal   Curvature  —  its  origin.  —  Next  to  the 
ribs,   the   spinal  column   is  most  liable   to  permanent 
deformity  from  compression.     We  have  already  spoken 
of  the  stooping  attitude,  acquired  at  study  or  in  follow- 
ing sedentary  employments,  but  a  greater  danger  is  to 
be  apprehended  from  a  lateral   or  sidewise   curvature, 
induced  by  working  at  occupations  which  employ  but 
one  hand  and  arm. 

The  constant  action  of  the  muscles  on  one  side,  while 
those  of  the  other  remain  inactive,  will  naturally  tend 
to  draw  the  dorsal  portion  of  the  spine  toward  that  side. 
This  tendency  is  often  aided  by  an  elevated  position 
of  the  elbow  of  the  active  arm,  or,  in  many  instances, 
merely  by  a  habit  of  drawing  the  shoulder  of  that  side 
upward.  This  deformity  is  very  common,  to  a  greater 
or  less  extent,  among  needle-women,  and  is  frequently 
seen  among  clerks  who  write  at  high  desks.  The  de- 
formity is  often  so  slight  as  to  escape  the  notice  of 
those  suffering  from  it,  or  their  friends,  and  yet  it 
always  impairs  the  powers  of  endurance. 

338.  Exercise  —  its  effects.  —  In  adult  age  the  bones 
become  firm  and  solid,  and  are  much  less  liable  to  be 
distorted  or  deformed  by  pressure   than   in  early  life; 
they  are,  however,  subject  to  the  general  law  of  waste 
and  repair  common  to  all  parts  of  the  living  machinery. 
This  transformation  takes  place  more   slowly  in  bone 
than  in  the  soft  parts,  but  the  health  of  the  bone  re- 
quires that  it  be  carried  on  steadily  and  at  a  uniform 
rate.     This  demands  active  exercise  in  a  good  atmos- 
phere. 

B.  P.— 20. 


232  HYGIENE. 

It  has  been  demonstrated  that  the  bones  actually 
diminish  in  size,  when  persons  accustomed  to  active 
labor  suddenly  change  their  habits  of  life  and  abandon 
their  activities.  But  exercise  may  be  carried  to  ex- 
haustion, and  both  bone  and  muscle  may  be  diminished 
in  size  and  impaired  in  strength  by  overwork. 

Recapitulation. 

Bone  nutrition  demands  food  sufficiently  rich  in  phosphate 
of  lime.  Oversupply  renders  them  brittle.  Deformity  of  the 
skeleton  may  result  from  unnatural  positions  long  continued. 
Freedom  of  motion  and  frequent  change  of  attitude  are  neces- 
sary to  secure  a  well-developed  frame.  Deformities  are  more 
easily  produced  in  childhood  than  in  mature  age.  Spinal  curva- 
ture—how induced,  and  its  effect  on  the  general  health. 


LESSON    XLII. 

MUSCULAR  EXERCISE. 

339.  Muscular  Motion.  —  The  system  of  muscles, 
with  their  tendons  and  attachments,  constitute  the 
machinery  of  motion,  which  is  operated  by  the  vital 
force  through  the  motor  nerves.  A  general  law,  gov- 
erning all  the  vital  machinery,  provides  that,  Avithin 
certain  limits,  an  organ  shall  correspond  with  the  work 
it  is  required  to  do.  Under  this  law,  *the  muscles 
increase,  both  in  size  and  force,  by  their  judicious  use, 
and  the  supply  of  vital  energy  is  correspondingly 
augmented. 

When   the   muscles   are   brought   into   use,  there  is 


MUSCULAR  EXERCISE.  233 

an  increased  flow  of  blood  to  them,  which  demands  a 
corresponding  increase  in  the  action  of  the  whole  cir- 
culatory apparatus;  but  this  augmented  circulation 
throws  more  blood  to  the  lungs  to  be  purified  and 
aerated,  and  this  requires  fuller  and  deeper  breathing. 
A  larger  flow  of  oxidized  blood  being  transmitted 
through  the  capillaries,  the  chemical  changes,  both  in 
the  tissues  themselves  and  in  the  combustible  elements 
of  the  food,  are  directly  increased. 

340.  Influence  of  Exercise.  —  Now  this  complicated 
chain  of  causes  and   effects,  springing  from  muscular 
contraction,  terminates  in  two  important  results:  first, 
the  cell  structure  of  the   muscles  themselves   is  more 
frequently  renewed,   by  which    means  the  contraction 
of  the   muscle  is  rendered   more   efficient;    and  if  the 
demand  is   kept  up  by  habitual  activity,  the  number 
of  cells  will  be  increased,  thus  giving  greater  volume 
and  density  to  the  muscles  that  are  in  frequent  use. 

In  the  second  place,  the  chemical  change  connected 
with  the  renewing  of  the  tissues — the  removal  of  the 
old  matter  and  depositing  of  the  new,  as  well  as  the 
rapid  oxidation  of  the  carbon  and  hydrogen  of  the 
food — is  directly  connected  with  the  evolution  of  vital 
force.  This  not  only  serves  to  increase  the  power  of 
muscular  contraction,  but  it  re-inforces  all  the  vital 
functions  and  imparts  activity  to  the  mind. 

341.  Muscular  Activity  and  Good  Health. — This 
activity  of  the  muscular  apparatus,  terminating  in  an 
increased   waste   of   material,   with    a   correspondingly 
augmented  force  distributed  to  all  the  organs,  calls  for 
a  supply  of  new  material  to  be  furnished  by  the  di- 
gestive   apparatus.      This   is   the  only  legitimate   ind 


234  HYGIENE. 

natural  means  of  creating  an  appetite ;  for  it  not  only 
demands  the  food,  but  at  the  same  time  supplies  the 
force  for  its  speedy  and  perfect  digestion.  But  while 
it  furnishes  vital  force  for  the  digestion  of  the  addi- 
tional food  demanded,  this  is  only  the  measure  of  the 
augmented  vital  force  of  all  the  organs.  Muscular  ac- 
tivity is,  therefore,  to  be  regarded  as  the  first  link  in 
the  chain  of  phenomena  leading  to,  and  securing  that 
very  desirable  result,  good  health.  More  or  less  directly 
connected  with  a  vigorous  exercise  of  the  muscles, 
stands  the  healthy  performance,  correct  habit,  and 
persistent  endurance  of  all  the  functions  of  life. 

342.  Exercise  as  a  corrective.  —  If  a  person  has 
contracted   a   vicious   habit   of   imperfect    and   shallow 
breathing,  vigorous    exercise  will    soon    compel   a  free 
and  full  use  of  the  lungs,  and  directly  establish  a  more 
correct  habit  of  breathing.      If  sedentary  employments 
endanger   a   curvature   of   the   spine,   a  brisk   walk   of 
half  an  hour,  once  or  twice  a  day,  will  be  found  the 
most  effectual  remedy.     The  almost  instant  fatigue  of 
walking  in  a  bent   posture  will  compel  the  erect  atti- 
tude as  a  means  of  relief. 

But  muscular  exercise  has  its  healthful  restrictions. 
It  should  never  be  violent,  nor  should  it  be  continued 
to  fatigue.  Whatever  form  of  exercise  may  be  selected, 
the  action  should  commence  moderately  and  be  gradu- 
ally increased  to  the  proper  intensity.  Active  forms  of 
exercise  should  not  be  suddenly  suspended;  and  if  the 
exercise  has  produced  perspiration,  additional  clothing 
should  be  put  on. 

343.  Pure  Air   for   Exercise. —  Exercise   should  be 
conducted  in  the  open  air,  if  we  would  derive  from  it 


MUSCULAR  EXERCISE.  235 

the  greatest  benefit.  If  the  air  we  breathe  be  vitiated 
by  a  mixture  of  unwholesome  gases,  or  if  its  proper 
'proportion  of  oxygen  be  reduced  by  having  been  pre- 
viously breathed,  the  good  effect  of  exercise  on  the 
vital  force  is  lost,  and  even  a  positive  injury  may  be 
the  result. 

Muscular  activity  can  be  continued  longer  in  the 
open  air,  without  producing  a  sense  of  fatigue,  than 
in  a  close  room.  An  invalid  will  sit  up  longer  when 
riding  in  a  carriage,  than  in  an  easy  chair  in  the  sick- 
room. If,  however,  the  condition  of  the  weather  forbids 
out-door  exercise,  or  circumstances  render  it  inconven- 
ient, the  windows  may  be  thrown  open  and  the  room 
freely  ventilated,  so  that  a  good  substitute  for  the  free 
air  of  out-doors  may  be  had,  which  will  be  much  better 
than  omitting  the  exercise. 

344.  Sunlight.  —  Light  exerts  a  curious  influence  on 
the  ability  to  endure  exercise  without  suffering  fatigue.  • 
Repeated  experiments  have  demonstrated  that  persons 
can  endure  labor  with  less  fatigue  in  the  sunshine 
than  in  the  shade,  the  temperature  being  the  same. 
We  shall,  perhaps,  never  know  how  the  sun's  rays 
impart  force  to  both  vegetable  and  animal  life,  but 
the  fact  may  be  ascertained  every  day. 

Kitchens  and  workshops  should  be  well  lighted,  as 
well  as  ventilated,  and  living-rooms  should  be  on  the 
sunny  side  of  the  house,  and  the  light  should  be  freely 
admitted.  Miners,  and  others  who  work  by  artificial 
light,  are,  as  a  general  rule,  short-lived,  and  have  a 
feebler  vitality  than  those  who  enjoy  sunshine.  In- 
valids, and  persons  confined  by  chronic  forms  of  disease, 
should  have  light,  cheerful  rooms. 


236  HYGIENE. 

345.  Amount  of  Exercise.  —  Exercise,  whether  in 
the  form  of  manual  labor,   or    taken   expressly  for  its 
sanitary    effect,    should    be    reduced    to    a    habit,    and 
should   have   its   regular   periods   of  activity  and  rest. 
The   amount   of  exercise   necessary  to  secure    its   best 
effect   is   modified  by  so  many  circumstances,  that  no 
special  rule  can  be  given.     The  general  law  governing 
exercise,  as  we  have  elsewhere  said,  is  that  it  is  bene- 
ficial up  to  the  point  of  fatigue;   but  as  soon  as  this 
feeling  is  distinctly  perceived,  exercise  should  be  sus- 
pended at  once. 

Persons  who  are  beginning  a  course  of  active  exercise 
will  soon  reach  this  point,  but  each  succeeding  day 
they  will  find  themselves  able  to  continue  the  exercise 
longer,  and  even  add  to  its  force  and  activity,  until 
eight  or  ten  hours  of  the  day  may  be  devoted  to 
active  labor,  without  materially  impairing  the  vital 
energy.  Fatigue  is  more  readily  induced  by  the  vio- 
lence of  the  exercise  than  by  its  long  continuance.  A 
person  who  will  walk  a  mile  in  thirty  minutes  and 
feel  no  fatigue,  will  be  entirely  exhausted  after  run- 
ning that  distance  in  ten  minutes. 

346.  Mental  Functions  and  Exercise. — The  mental 
condition  during  exercise  is  of  the  first  importance  in 
regard  to  its  sanitary  value.     If  exercise  be  imposed  as 
a  daily  task  —  if  it  be  taken  as  a  medicine  to  secure 
health,  it  will  soon  become  irksome,  and  even  repul- 
sive, and  no  good  will  be  derived  from  it.     Whatever 
may  be  the  form  of  exercise,  the  mental  action  should 
be  directed  to  some  other  point  than  that  of  the  mere 
muscular  motion. 

If  walking  is  selected,  the  mind  should  be  pleasantly 


EXERCISE  AND  KEST.  237 

employed  on  some  subject  entirely  disconnected  from 
the  exercise  itself.  The  muscular  movements  of  walk- 
ing should  be  performed  entirely  by  the  reflex  action 
of  the  spinal  cord. 

Recapitulation. 

Judicious  exercise  increases  both  the  volume  and  force  of 
muscles.  It  hastens  the  renewal  of  the  tissues,  and  thus  con- 
duces to  good  health.  Exercise  should  be  in  the  open  air 
when  possible,  for  in  a  vitiated  air  it  soon  produces  fatigue. 
Sunlight  has  an  invigorating  influence  on  all  the  vital  func- 
tions. Exercise  should  be  habitual,  and  the  attention  should 
be  directed  to  some  other  object. 


LESSON    XLIII. 

EXERCISE    AND    REST. 

347.  Rules  of  Exercise.  —  Summing  up  what  has 
been  said  on  the  subject  of  exercise,  we  present  the 
following  rules,  namely: 

1st.  It  should  call  into  play  the  largest  number  of 
muscles,  and  include  such  a  variety  of  attitudes  and 
motions  as  to  distribute  the  exercise  over  the  whole 
body. 

2d.  The  movements  should  be  energetic  and  active, 
but  never  violent. 

3d.  The  exercise  should  carry  with  it  some  mental 
stimulant,  or  it  should  leave  the  mind  free  to  employ 
itself  on  other  subjects  without  interfering  with  the 
muscular  movements.. 


238  HYGIENE. 

4th.  It  should  be  regular  and  habitual. 

5th.  It  should  have  the  full  advantage  of  free  air 
and  light. 

6th.  It  should  begin  gradually,  and  be  increased  to 
full  energy. 

7th.  All  kinds  of  exercise  should  be  avoided  which 
require  the  muscles  to  be  held  long  in  a  state  of  rigid 
contraction. 

348.  Gymnastics. — In  selecting  a  form  of  exercise  to 
fill  these  indications,  we  have  a  wide  field  in  which  to 
make  our  choice ;  and  yet  but  few  of  the  special  modes 
which  have  been  invented  and  prescribed  as  sanitary 
measures,  are  free   from  formidable   if  not  fatal  objec- 
tions.     The    various    forms    of    gymnastics    and   calis- 
thenics,   while    they    fill    most    of    the    requirements, 
fail    to   furnish    any   mental    stimulus   other   than   the 
muscular    movements    themselves;    and    yet  these  de- 
mand  so  much   of  the   attention,  that   the   mind   can 
not  leave  the  movements  to   seek   other   fields  of  em- 
ployment. 

The  various  games  of  ball,  etc.,  while  they  call 
into  activity  a  wide  range  of  muscles,  and  have  the 
advantages  of  open  air  and  ample  light,  and,  withal, 
furnish  a  vigorous  mental  stimulant  in  the  chances 
of  the  game,  yet  there  is  a  constant  tendency  for 
that  activity  to  be  converted  into  violence,  that  may 
end  in  actual  injury,  and  more  than  defeat  the  object 
of  the  exercise. 

349.  Manual  Labor. — Walking,  when  properly  per- 
formed, is  one  of  the  most  healthful  forms  of  exercise, 
and  one  which  is   nearly  always  available.     We  said, 
when  properly  performed,  for  every  body  has  not  learned 


EXERCISE  AND  REST.  239 

to  walk  correctly.  A  promenade  should  always  be  per- 
formed in  the  open  air,  with  the  body  and  head  erect, 
and  the  shoulders  thrown  back  so  as  to  give  free  ex- 
pansion to  the  lungs.  The  clothing  should  be  adapted 
to  the  condition  of  the  weather,  and  should  be  so  ad- 
justed as  to  permit  the  free  use  of  every  muscle  of  the 
body,  without  compression  or  restraint. 

But  the  demand  for  active  exercise  finds  its  legiti- 
mate and  complete  fulfillment  in  the  various  forms  of 
useful  labor.  This  is  demonstrated  every  day  in  the 
fact  that  the  most  perfect  symmetry  of  form  and  vigor 
of  constitution  is  found  among  those  who  spend  most 
of  their  waking  hours  in  manual  labor.  Labor  only 
requires  to  be  regulated  by  a  proper  knowledge  and 
correct  application  of  physiological  laws,  to  meet  all 

the  demands  of  healthful  exercise. 

-»* 

350.  Kinds  of  Labor  not  Healthy.— But  all  forms 
of  labor  are  not  alike  promotive  of  health.  That  form 
of  it  is  best  which  furnishes  the  greatest  variety  and 
widest  range  of  activities.  These  conditions  are  found 
in  the  highest  perfection  in  agricultural  and  horticul- 
tural pursuits.  The  division  of  labor  which,  in  our 
modern  civilization,  has  been  carried  to  so  great  an 
extent,  and  which  has  resulted  in  such  a  wonderful 
economy  of  labor,  has  a  direct  tendency  to  reduce  its 
value  as  a  means  of  maintaining  good  health. 

The  tendency  of  this  system  is  to  confine  the  work 
to  the  repetition  of  a  few  motions — the  activity  of  a 
part,  and  often  but  a  small  part  of  the  body ;  and  while 
these  organs  are  generally  overworked,  the  remainder 
of  the  body  becomes  feeble  from  disuse.  Some  occu- 
pations employ  the  hands  alone,  while  the  other 
B.  P.— 21. 


240  HYGIENE. 

muscles  of  the  body  are  unused  and  the  brain  unem- 
ployed. Such  occupations  are  pernicious  to  health, 
and  should  be  avoided. 

351.  Bad   effects   of  Overexercise. —  But    exercise, 
like  every  other  good  thing,  is  liable  to  be  abused,  and 
thus  become  a  positive  injury  and  a  fruitful  source  of 
disease.     It  is  only  when  labor  is  perverted  that  it  de- 
generates into  drudgery  and  becomes  a  curse,  destroy- 
ing the  symmetry  of  the  body,  entailing  on  its  victim 
disease  and  suffering,  and  greatly  reducing  the  period 
of  human  life. 

The  tendency  of  modern  society  is  to  inflict  positive 
injury  on  a  large  class,  by  idleness  and  want  of  any 
healthful  exercise,  and  to  break  down  the  constitution 
and  ruin  the  health  of  another  class  by  overwork. 
Eight  hours  of  labor — active,  but  not  violent — with  an 
interval  of  one  or  two  hours'  rest,  will,  in  most  consti- 
tutions, be  endured,  without  loss  of  energy  or  injury  to 
health,  for  six  clays  in  succession,  and,  with  a  day  of 
rest  intervening,  may  be  repeated  from  week  to  week 
indefinitely.  A  few  may  endure  more  than  this,  but 
these  are  the  exceptions  and  not  the  rule. 

352.  Exercise  for  Young  Persons. — Young  persons 
in   active   employments   need   more   frequent  intervals 
of  rest   than    those   of  mature   age;    and   the   same    is 
true  in  regard  to   exercise,  if  confinement   is  the  rule. 
Pupils   required    to   remain   quiet    in    the   school-room, 
should  have  at  least   fifteen  minutes  of  active  exercise 
at  the  end  of  each  hour.     Such  a  course  would  not  only 
secure  better  health  to  the  scholars,  but  a  more  satisfac- 
tory progress  in  their  studies. 

Persons  laboring  in  shops  will  greatly  improve  their 


EXERCISE  AND  BEST.  241 

health  by  devoting  an  hour  each  day  to  amusement 
in  the  open  air  and  sunlight.  This  is  especially  true 
of  those  occupations  which  employ  only  the  hands,  or, 
possibly,  only  a  single  hand.  Such  persons  require 
as  much  exercise  of  the  whole  body  as  their  health 
would  demand  if  they  were  actually  unemployed. 
Boys  generally  manage  to  get  exercise  enough;  and 
if  girls  from  fourteen  to  twenty  years  of  age  were 
compelled  to  exercise  every  day  in  the  open  air,  we 
should  soon  have  a  different  race  of  women. 

353.  Rest — its  necessity. —  But  vital  machinery  is 
not  made  for  constant  activity.     A  regular  alternation 
of  action  and  rest  is  the  law  of  life  every- where,  and 
the  intervals  of  repose  are  as  essential  to  health  as  are 
the    periods   of  activity.      Rest    is    rendered   necessary 
from  two  considerations:    In   the   first   place,  the  cells 
composing   the   muscular   fibers  are   broken  down   and 
removed  more  rapidly  during  the  active  contraction  of 
the  muscle,  than  the   nutritive   process   is   able   to  re- 
place them;  but  while  we  rest,  the  preponderance  is  on 
the   other  side — -the   wastes   are    replenished   and   the 
muscular  tissue  restored  to  its  original  integrity. 

In  the  second  place,  active  exercise  expends  force 
more  rapidly  than  it  can  be  supplied  by  the  brain  and 
nerves:  hence,  as  fatigue  comes  on,  the  muscles  con- 
tract more  slowly  and  witb  less  energy,  until  finally 
the  entire  exhaustion  of  strength,  above  what  is  neces- 
sary to  keep  in  motion  the  involuntary  organs,  takes 
place,  and  motion  ceases  from  prostration  of  the  vol- 
untary powers. 

354.  Two   kinds  of  Rest. — Corresponding   to   this 
division,   rest   must  be   of  two   kinds,   looking   to   the 


242  HYGIENE. 

accomplishment  of  these  two  objects.  A  mere  suspen- 
sion of  muscular  contraction  is  all  that  is  necessary  to 
restore  the  wasted  tissues,  for  nutrition  will  go  on 
with  an  activity  stimulated  by  the  demand  for  new 
matter,  while  the  waste  from  action  will  be  suspended. 
Under  these  influences,  but  a  short  period  of  repose 
will  be  required  to  restore  the  equilibrium. 

That  rest  is  most  perfect,  however,  which  most 
completely  suspends  muscular  action;  and  from  this 
it  follows,  that  a  reclining  position  is  better  adapted 
to  rest  than  either  sitting  or  standing.  But  to  restore 
exhausted  contractile  force,  requires  more  than  mus- 
cular repose :  it  demands  brain  rest,  which  can  only 
be  had  in  sleep. 

Recapitulation. 

General  rules  for  exercise.  Gymnastics  do  not  furnish  any 
mental  stimulus  other  than  the  muscular  movements  them- 
selves. Walking  is  a  healthy  and  available  form  of  exercise. 
Manual  labor  properly  regulated  is  most  conducive  to  health. 
Kinds  of  labor  which  are  to  be  avoided.  Rest  must  follow 
activity.  Muscular  rest,  distinguished  from  brain  rest. 


\ 

LESSON    XLIV. 

BRAIN   REST. 

355.  The  Nervous  System.  —  The  systems  of  nutri- 
tion and  voluntary  motion,  which  we  have  been  con- 
sidering, are  entirely  dependent  on  the  nervous  system 
for  the  supply  of  force  necessary  for  their  several 
functions.  All  the  diseases  of  these  systems  which 


BKAIN  BEST.  243 

do  not  depend  on  structural  derangements  of  the 
organs,  are  therefore  to  be  traced  to  disturbances  in 
the  nervous  system. 

But  this  dependence  is  reciprocal.  The  brain  de- 
pends on  the  digestive  apparatus  for  a  constant  supply 
of  healthy  blood,  rich  in  the  elements  of  brain  nutri- 
tion. It  is  also  dependent  on  the  uninterrupted  action 
of  the  respiratory  organs,  for  a  supply  of  oxygen  neces- 
sary to  carry  forward  the  chemical  changes  so  inti- 
mately connected  with  the  evolution  of  that  vital  force. 
Without  the  chemical  changes  dependent  on  digestion 
and  respiration,  the  supply  of  vital  force  is  cut  off; 
and  without  a  healthy  action  of  the  brain  and  nerves, 
its  distribution  is  impossible. 

356.  Brain  needs  Exercise.  —  The  brain  and  its 
appendages  are  subject  to  the  general  physiological 
law  of  alternate  activity  and  rest,  which  is  so  inti- 
mately connected  with  the  normal  condition  and 
healthy  action  of  all  the  other  organs  of  the  body. 
As  the  brain  is  the  most  delicately  organized  part  of 
the  body,  and  receives  proportionally  the  largest  supply 
of  blood,  its  tissues  are  transformed  with  a  correspond- 
ing rapidity. 

If  the  exercise  of  brain  be  regular,  and  not  too 
violent  nor  too  long  protracted,  and  the  nutrition  be 
sufficient  to  supply  the  material  wasted  by  the  activity, 
the  result  of  the  exercise  will  be  the  same  here  as  else- 
where. The  efficiency  of  brain  action  will  be  in  pro- 
portion to  the  frequent  and  perfect  renewal  of  its  cell 
structure.  The  functions  of  sensation  and  motion  do 
not  exhaust  the  cerebrum  as  rapidly  as  the  function 
of  thought. 


244  HYGIENE. 

357.  Brain    fatigue.  —  During    our    waking   hours, 
there  is  hardly  such  a  thing  possible  as  absolute  brain 
rest.     The  attention  is  constantly  called  to  the  various 
objects  of  sense  around  us,  and  the  perceptive  faculty  is 
as  constantly  required  to  note   the  various  sensations, 
so   that  the  representative  faculty  can   recall    them   at 
pleasure. 

It  is  true  that,  under  ordinary  circumstances,  this 
action  is  so  nearly  spontaneous  that  it  can  hardly  be 
called  brain  labor.  But  let  a  person  spend  a  day  in 
sight-seeing,  in  some  new  and  interesting  locality,  or 
listen  closely  for  an  hour  or  two  to  an  intricate  argu- 
ment, or  an  elaborate  discourse  on  any  subject  that 
secures  his  attention,  and  a  sense  of  brain  weariness 
will  be  felt.  The  undivided  attention  can  no  longer  be 
fixed  and  held  to  the  subjects  of  observation,  and  the 
mind  will  fail  to  grasp  the  scope  of  the  argument,  or 
perceive  the  nice  distinctions  which  the  speaker,  from 
familiarity  with  his  subject,  may  present  even  with 
great  clearness. 

358.  Brain  weariness. — This  point  of  mental  fatigue, 
or  brain  weariness,  is  induced  more  readily  in  young 
persons  than  in  those  of  mature  age,  and  in  that  class 
who  are  not  accustomed  to  brain  work,  than   in  those 
whose  business  has  been  study.     This  fact  is  especially 
commended  to  the  notice  of  parents  and  teachers. 

Pupils,  at  the  immature  age  of  ten  or  twelve  years, 
are  required  to  confine  their  attention,  often  for  a 
period  of  eight  hours  a  day,  to  studies  which  are 
frequently  abstruse,  uninteresting,  and,  to  them,  diffi- 
cult; and  this,  generally,  with  but  very  brief  intervals 
of  rest.  After  an  hour  or  less  of  close  application  to 


BRAIN  BEST.  245 

study,  if  the  pupil  be  required  to  divert  the  brain 
action  in  the  direction  of  brisk  muscular  exercise, 
involving  chiefly  the  functions  of  the  spinal  cord,  the 
brain  will  return  to  its  task  refreshed,  and  in  this 
manner  it  may  labor  safely  and  profitably  five  or  six 
hours  a  day. 

359.  Mental  effort  long  continued.  —  After  a  period 
of  close  mental  application,  if  the  pupil  finds  himself 
unable   to  confine   his  attention  to  the   subject  of  his 
investigation,  or  discovers  an  inability  to  exercise  his 
ordinary  powers   of   mental    perception,   he    should   be 
admonished  at  once  and  intermit  his  labors.     All  exer- 
tion beyond  this  point  is  more  than  a  waste  of  time 
and   effort;    it    is    inflicting   a   positive   and,   to   some 
extent,  a  permanent  injury  on  the  brain.     If  exertion 
be   persisted   in    after   this   stage,    a   condition    of   ex- 
haustion will  follow,  from  which  recovery  can  be  found 
only  in  sleep.    But  sound,  refreshing  sleep  is  riot  always 
attainable  under  these  circumstances. 

The  system  of  cramming,  which  is  becoming  so 
coiiimon  in  our  schools,  and  which  prescribes  for  pupils 
of  tender  age  an  amount  of  mental  labor  that  would 
be  more  than  enough  for  well  matured  and  disciplined 
minds,  has  a  tendency  to  arrest  mental  development 
by  overwork. 

360.  Time  of  Study.  —  No  general  rule  can  be  laid 
down  prescribing  a  definite  number  of  hours  of  mental 
labor  to  each  pupil  in  a  school.     So  many  modifying 
circumstances  may  interpose,  such  as  age,  sex,  genefal 
health,    temperament,    previous   habits   of   study,    etc., 
that    the    whole    matter    must    be    left    to    parents   or 
teachers,    to   be    governed    by   their   judgments    under 


246  HYGIENE. 

very  broad  instructions.  Before  the  age  of  ten  years, 
study  should  be  amusement  rather  than  business;  be- 
tween ten  and  fifteen  years,  the  confinement  should 
not  exceed  an  hour  of  close  application  without  inter- 
mission. 

As  a  general  rule,  boys  endure  confinement  to  study 
better  than  girls,  and  persons  of  bilious  better  than 
those  of  a  nervous  temperament;  but  those  who  are 
least  able  to  sustain  a  protracted  effort,  can  generally  ac- 
complish more,  by  close  application,  in  a  given  time,  than 
those  who  suffer  less  from  long  continued  mental  labor. 

361.  Special  Training.  —  In  cultivating  and  devel- 
oping the  mental  powers,  the  same  law  governs  the 
process  as  that  which  controls  the  education  and  train- 
ing of  muscular  movements.  If  the  entire  attention  be 
directed  to  the  training  necessary  to  the  performance 
of  a  single  motion  or  group  of  motions,  great  perfection 
may  be  attained  in  that  direction;  but  all  the  other 
movements  being  neglected,  the  aggregate  of  muscular 
power  is  reduced,  and  the  educated  faculties  soon  fail 
for  want  of  the  force  which  can  be  evolved  only  in  the 
symmetrical  development  of  all  the  faculties. 

Conforming  to  this  law,  it  follows  that,  if  the  mental 
faculties  be  educated  in  a  single  direction,  a  much 
higher  perfection  is  attainable,  in  that  particular  line, 
than  would  be  possible  if  the  culture  and  training 
were  distributed  equally  among  all  the  faculties.  But 
the  few  favored  faculties,  depending  on  the  general 
brain  force  for  the  power  of  their  expression,  and  this 
failing  through  neglect  of  general  culture,  soon  reduce 
the  overtrained  powers  to  the  imbecility  of  the  neglected 
faculties. 


BRAIN  REST.  247 

362.  Relation  of  Mind  to  Matter.  —  Many  well- 
disposed  persons  object  to  referring  the  mental  mani- 
festations, in  any  case,  to  the  proper  development  and 
healthy  action  of  the  brain,  because  of  a  supposed  tend- 
ency to  materialism.  But  the  relation  of  mind  to 
matter  is  a  question  of  fact,  and  is  independent  of  all 
theory. 

Nothing  is  clearer  than  that  all  our  knowledge  of  an 
outer  world,  as  well  as  our  knowledge  of  the  thoughts 
and  actions  of  other  minds,  reach  us  through  sensation ; 
and,  on  the  other  hand,  that  we  can  transfer  our 
thoughts  to  other  minds  only  by  muscular  motion. 
But  sensation  and  motion  are  primary  brain  functions. 
There  is  no  necessity,  however,  for  confounding  the 
agent  which  operates,  with  the  instrument  by  means 
of  which  the  operation  is  performed. 

Recapitulation. 

There  is  a  mutual  dependence  between  the  brain  and  the 
other  organs  of  the  body.  All  vital  action  is  dependent  on  a 
healthy  condition  of  the  brain.  The  brain  requires  exercise  in 
order  to  maintain  its  powers  of  action.  Of  the  three  brain 
functions,  thought  is  the  most  exhausting.  Brain  labor  de- 
mands frequent  intervals  of  rest.  Protracted  study  most  in- 
jurious to  young  persons.  Special  training  operates  unfavorably 
on  the  general  development  of  mind. 


248  HYGIENE. 


LESSON    XLV. 

BRAIN    POISONS. 

363.  Alcohol,   Tobacco,   and   Opium.  —  It   may   bo 

regarded  as  an  axiom  in  hygiene,  that  the  proper  devel- 
opment and  healthy  action  of  the  brain  and  nerves,  in  the 
absence  of  structural  derangements  in  the  other  organs,  is 
the  prime  condition  of  good  health.  This  being  true,  it 
follows  that  our  first  care  in  the  preservation  of  health 
is  to  guard  well  the  brain,  supply  it  with  pure,  well 
aerated  blood,  give  it  the  proper  alternations  of  exer- 
cise and  rest  in  each  of  its  threefold  functions,  and 
preserve  it  from  the  influence  of  poisons  which  impair 
its  powers,  disturb  its  functions,  or  derange  its  delicate 
structure. 

Of  this  class  of  poisons  the  most  dangerous  are  alco- 
hol, opium,  and  tobacco.  Twro  of  these,  at  least,  are  in 
common  use  in  this  country,  and  the  third  (opium)  is 
rapidly  gaining  favor  with  certain  classes  in  American 
society.  If  we  had  the  means  of  tracing  to  its  legiti- 
mate source  every  disease  that  afflicts  civilized  rnan, 
we  have  no  doubt  but  that  a  large  majority  would  be 
found  to  originate,  either  directly  or  indirectly,  in  the 
habitual  use  of  these  narcotics. 

364.  Alcohol  —  its  chemical  relation.  —  Alcohol  is 
the    most   active,  and   on   this   account,  as   well  as  on 
others    that    will    appear    hereafter,    it    is    the    most 
dangerous    of    this    class    of    poisons.      Alcohol    is   the 
product  of  fermentation;    the  result  of,  or,  rather,  one 
of    the    bodies    resulting    from,    the    decomposition    of 
sugar.     If   it    is    produced   from    grain,    potatoes,    etc., 


BRAIN  POISONS.  249 

the  starch  is  first  converted  into  sugar,  and  this  into 
alcohol  and  carbonic  acid :  the  one  a  poison  when  taken 
into  the  stomach,  the  other  a  most  deadly  poison  when 
inhaled. 

In  all  the  various  forms  of  intoxicating  liquors,  the 
active  agent  is  alcohol;  and  the  effect  of  a  given  quan- 
tity of  it  is  the  same,  whether  in  the  concentrated  form 
of  distilled  liquors,  such  as  brandy,  rum,  gin,  or  whisky, 
or  in  the  milder  dilutions  of  fermented  mixtures,  such 
as  wine,  beer,  cider,  etc.  In  all  these  mixtures  the 
fluids  with  which  it  is  mixed  serve  only  as  solvents 
of  the  alcohol,  and  do  not  decompose  it  nor  change  its 
character. 

365.  Alcohol    and   Organic   Substances.  —  Though 
alcohol    produces  its  chief  and  most  observable   effect 
directly  on  the  great  nervous  centers,  yet  there  is  an 
indirect  action  through  the  nutritive  functions,  which 
is  too  important  to  be  overlooked.     The  chemical  action 
of  alcohol  is  to  arrest  or  impede  change  in  organic  sub- 
stances wherever  it  comes  in  contact  with  them. 

Animal  tissues  may  be  preserved  in  alcohol  for  an 
indefinite  period,  so  as  to  be  entirely  proof  against 
the  putrefactive  process.  Vegetable  substances,  also, 
may  be  preserved  from  decay  indefinitely  by  immer- 
sion in  alcohol.  But  the  life  processes,  from  the  first 
stage  of  digestion  to  the  completed  work  of  trans- 
forming the  tissues,  is  incessant  change;  and  whatever 
interferes  with  this  regular  succession  of  chemical  trans- 
formations, in  the  same  proportion  disturbs  the  vital 
functions  and  impairs  health. 

366.  Alcohol   is  Indigestible.  —  The   first   effect  of 
alcohol,   when    taken    into   the   stomach,   is   to   impair 


250  HYGIENE. 

the  capability  of  change  in  the  food  in  the  process 
of  digestion,  for  digestion  consists  of  a  series  of  chem- 
ical changes.  Beefsteak  that  has  been  macerated  in 
alcohol  for  forty-eight  hours  is  perfectly  indigestible. 
Although  the  brandy  taken  at  dinner  impairs  di- 
gestion while  it  is  present  in  the  stomach,  yet  a 
wise  provision  is  made  by  which  the  stomach  is  soon 
relieved  of  its  presence. 

Alcohol  is  entirely  indigestible,  and  does  not  pass 
with  the  chyme  into  the  intestinal  tube,  but  is  in- 
stantly taken  up  by  the  absorbents  and  carried  into 
the  veins,  and  by  way  of  the  right  side  of  the  heart 
and  pulmonary  artery,  it  reaches  the  lungs  and  begins 
to  escape  with  the  breath  exhaled.  That  which  gives 
odor  to  the  breath  of  one  who  drinks  is,  substantially, 
pure  alcohol.  A  very  small  part  of  it  has  lost  one- 
third  of  its  hydrogen,  and  is  converted  into  a  compound 
which  chemists  have  named  aldehyde. 

367.  Alcohol  impairs  Chemical  Change.  —  Though 
the  odor  of  alcohol  can  be  detected  on  the  breath  in  a 
few  minutes  after  it  has  been  taken  into  the  stomach, 
yet  it  is  not  all  disposed  of  so  soon,  for  the  odor  fre- 
quently remains  on  the  breath  for  twenty-four  hours. 
All  this  time  the  poison  has  been  mixed  with  the 
blood,  and  passing  the  capillary  circulation,  it  has 
produced  its  specific  effect  on  the  changes,  so  inti- 
mately connected  with  life  itself,  going  on  in  this 
region  of  waste  and  repair.  These  changes  consist  in 
the  oxidation  of  the  carbon  and  hydrogen  of  the  di- 
gested food,  and  the  consequent  evolution  of  animal  heat 
and  vital  force. 

That   it   really   impairs  all  these  actions  and  dim- 


BKAIN  POISONS.  251 

inishes  change  in  the  capillaries,  and  consequently 
reduces  the  normal  amount  of  vital  force  by  which  the 
nervous  system  is  enabled  to  maintain  the  various 
voluntary  and  involuntary  motions  necessary  to  life, 
is  no  longer  a  matter  of  conjecture.  It  has  been  dem- 
onstrated that,  under  the  influence  of  alcohol,  the 
amount  of  carbonic  acid  exhaled  from  the  lungs  is 
diminished  from  thirty  to  fifty  per  cent. 

368.  Alcohol  lessens  Muscular  Force.  —  This  reduc- 
tion of  the  chemical  changes  going  on  in  the  capillary 
circulation   indicates   a   corresponding   change    in    the 
brain  force,  as  transmitted  by  way  of  the  motor  nerves 
to  the  muscles  by  which  the  various  movements  of  the 
body   are    performed.     This    deduction    of   science    has 
been  fully  demonstrated  by  repeated  experiments,  made 
by  actual  measurement  of  muscular  power  in  the  same 
individual  under  the  influence  of  alcohol  and  without 
it.     These    experiments    prove    that    the    reduction    of 
strength  is  very  accurately  measured  by  the  diminution 
of  carbonic    acid   from  the   lungs   in  breathing.     This 
reduced   supply  of  nervous  force   is   soon  apparent   in 
the  impaired  powers  of  endurance,  observed   in  those 
who  use  alcoholic  drinks. 

369.  Alcohol  causes  a  sense  of  heat.  —  The  effect 
of   alcohol    on    the    animal    heat    is   among   the    most 
curious   of   the    physiological    phenomena   that    attend 
its  action  on   the  living  body.     The   diminished   pro- 
duction  of  carbonic   acid,   when    under   the    influence 
of  alcohol,  would  suggest  a  reduced  combustion  in  the 
body,   and  a  corresponding   reduction   of  temperature; 
but  the  testimony  of  the  person  under  its  influence  is 
conclusive  in  the  opposite  direction;   he  avers  that  he 


252  HYGIENE. 

feels  warmer,  and  the  flush  of  the  blood  in  the   super- 
ficial vessels  appears  to  corroborate  his  testimony. 

Liebig,  the  justly  celebrated  German  chemist  and 
physiologist,  attempted  to  solve  the  mystery  by  sup- 
posing that  the  oxygen  inhaled  entered  into  combina- 
tion with  the  alcohol,  and  thus  produced  heat  without 
evolving  vital  force;  but  this  solution  will  require  an 
increased  amount  of  carbonic  acid  in  the  breath,  when, 
in  fact,  the  quantity  is  diminished. 

370.  The  Thermometer  shows  a  reduction  of  Tem- 
perature.—  But  the  mystery  disappears  at  once  when 
we  appeal  to  the  thermometer.  A  delicate  thermometer 
placed  under  the  tongue  will  show  an  unsteadiness  in 
the  temperature  for  the  first  fifteen  or  twenty  minutes 
after  taking  four  ounces  of  brandy.  In  some  instances 
the  temperature  falls  from  the  first,  but  in  most 
cases  there  is  an  increase  of  heat,  ranging  from  one- 
half  to  three-fourths  of  a  degree,  and  continuing  from 
ten  to  fifteen  minutes ;  after  which  there  is  a  reduction 
in  temperature  of  two  or  three  degrees,  lasting  for  sev- 
eral hours,  even  while  the  face  is  flushed  and  the  person 
affirms  that  he  is  warmer. 

But  common  observation  shows  that  he  will  freeze 
much  quicker  with  than  without  the  brandy.  The 
flush  of  his  face  is  the  result  of  diminished  action, 
suffering  the  blood  to  accumulate  in  the  capillaries; 
and  his  sense  of  heat  depends  on  perverted  sensi- 
bility. 

Recapitulation. 

Narcotics  operate  as  brain  poisons.  To  this  class  belong  alco- 
hol, tobacco,  opium,  etc.  Of  these,  alcohol  is  the  most  active.  It 
is  the  active  principle  of  all  spirituous  and  fermented  liquors. 


BRAIN  POISONS.  25& 

When  a  given  amount  is  taken,  its  effect  is  the  same,  whether 
concentrated  or  diluted. 

The  chemical  action  of  alcohol  on  organic  substances  arrests 
change.  This  impairs  digestion,  and  diminishes  vital  force. 
The  sense  of  heat  following  the  use  of  alcohol  is  the  result  of  de- 
ranged sensibility. 


LESSON   XLVI. 

BRAIN    POISONS — CONTINUED. 

371.  Narcotic  Poisons. — The  direct  action  of  alcohol, 
and  other  narcotic  poisons,  on  the  nervous  system  con- 
sists chiefly   in  diminished   sensibility   and  its  conse- 
quences.    If  the  mouth  be  filled  with  a  strong  alcoholic 
liquor,   such   as   brandy   or   whisky,   and  the  same  re- 
tained but  a  few  minutes,  it  will  be   found  that  the 
sense  of  taste  is  nearly,  if  not  entirely,  destroyed  for 
the  time  being. 

The  mucous  membrane  of  the  stomach  is  continuous 
with  that  of  the  mouth :  it  will,  therefore,  be  similarly 
affected  by  like  agents.  Alcohol  will  produce  a  double 
effect  on  digestion :  it  will  render  the  food  less  sub- 
ject to  change,  and,  therefore,  more,  difficult  of  diges- 
tion; and  it  will  so  .reduce  sensibility  in  the  nerves 
of  the  stomach  that  the  imperfectly  digested  food  will 
be  suffered  to  pass  the  pyloric  orifice  into  the  intestinal 
canal,  and  a  great  portion  of  the  food  be  lost,  if 
nothing  worse  occurs  from  the  presence  of  undigested 
food  in  the  intestines. 

372.  Alcohol   and  the   Digestive  Function.  —  But 


254  HYGIENE. 

this  abuse  of  the  stomach  can  not  be  long  indulged  in 
without  permanently  impairing  the  sensibility  of  that 
organ,  and  establishing  the  habit  of  imperfect  diges- 
tion, if  not  inducing  confirmed  dyspepsia.  The  first 
effect  of  this  impaired  digestion  is  a  demand  for  more 
food  than  would  be  required  if  digestion  was  perfect; 
for  it  is  not  the  amount  of  food  we  cat  that  repairs  the 
daily  wastes  of  the  body,  but  that  which  is  digested 
and  assimilated. 

This  increased  demand  for  food  after  taking  the 
"bitters"  is  often  mistaken  for  a  healthy  appetite,  and 
regarded  as  an  indication  of  increasing  tone  and  vigor 
in  the  digestive  apparatus.  If  the  alcohol  be  left  off, 
the  returning  sensibility  of  the  stomach  will  admonish 
the  brain  of  the  true  condition  of  that  organ,  and  its 
inability  to  digest  food,  and  consequently  it  will  refuse 
it,  a  loss  of  appetite  being  the  result. 

373.  Alcohol  impairs  sensibility. — The  diminished 
sensibility  in  the  nerves  of  the  stomach  is  not  a  local 
affection,  but  extends  to  the  whole  sentient  apparatus. 
It  is  to  this  fact  that  alcohol  owes  most  of  its  reputa- 
tion as  a  medicine.  It  renders  the  patient  insensible 
to  pain,  and  he  mistakes  this  insensibility  for  the  cure 
of  the  disease,  of  which  the  pain  was  but  the  warning 
of  a  faithful  sentinel.  The  insensibility  to  injury,  of 
those  who  are  intoxicated  is  very  commonly  noticed,  and 
illustrates  the  effect  of  this  poison  on  the  very  impor- 
tant function  of  sensation. 

The  general  sense  of  feeling  can  not  be  impaired 
without  the  local  senses  suffering  more  or  less.  Of 
these  the  sense  of  vision  early  feels  the  effect  of  the 
poison,  rather  in  a  perversion  of  vision  than  in  a  loss 


BRAIN  POISONS.  255 

of  sight.  To  intoxicated  persons,  things  often  appear 
double,  and  frequently  things  at  rest  appear  to  be  in 
motion.  The  sense  of  hearing  is  less  affected  by  alcohol 
than  the  other  senses,  and  yet  the  long  continued  use 
of  the  poison  often  seriously  impairs  that  faculty. 

374.  Exhilaration.  —  The    feeling    of    exhilaration, 
which  is  generally  mistaken  for  exalted  sensibility,  is, 
in  fact,  the  result  of  a  partial  paralysis  of  the  sentient 
extremities   of  the    nerves.      The    vital   force,    by   the 
movement  of  which  sensation  is  carried  on,  being  with- 
drawn from  the  nervous  expansions,  is  concentrated  on 
the   great   nervous   centers,   thus   manifesting  the  dis- 
turbed  equilibrium   of  nervous    force    rather   than  an 
increase  of  it. 

The  phenomenon  of  exhilaration  can  be  studied  better 
in  the  inhalation  of  chloroform,  or  nitrous  oxide,  than 
in  the  slower  process  of  administering  narcotics  by  the 
stomach.  The  exhilaration  is  the  same,  and  in  either 
case  the  power  to  feel  impressions  made  on  the  sentient 
nerves  is  diminished  from  the  beginning;  and,  if  car- 
ried far  enough,  terminates  in  total  insensibility,  un- 
consciousness, and,  finally,  in  death. 

375.  Fascinating  influence  of  Alcohol. —  This  ex- 
hilaration,   always    tending    toward    insensibility   and 
unconsciousness,  is  that  which  renders  alcohol  so  fas- 
cinating and  so  dangerous  a  poison.     Its  first  effect  is  to 
render  the  victim  unfit  to  judge  of  his  own  condition, 
of  the  nature  and  situation  of  things  around  him,  or  of 
his  relations  to  these  surroundings.     Through  the  me- 
dium of  the  general  nervous  sensibility,  we  determine 
our  condition  of  body  and  mind :  through  this  medium 

we  are   conscious  of  our  own   powers,   and  determine, 
B.  P. — 22. 


256  HYGIENE. 

with  a  good  degree  of  accuracy,  the  physical,  mental, 
and  moral  possibilities  and  duties  of  our  situation. 
But  the  moment  we  place  ourselves  under  the  exhila- 
rating influence  of  alcohol,  and  in  the  exact  ratio  in 
which  that  influence  affects  us,  we  lose  this  power. 
Our  judgment  of  ourselves,  of  our  powers,  and  of  our 
duties,  is  distorted  and  false,  and  this  false  judgment 
may  lead  us  to  ruin  our  health,  corrupt  our  morals, 
and  alienate  our  friends. 

376.  The   Action   of  Alcohol.  —  There    are    several 
fallacies  connected  with  the  too  common  indulgence  in 
alcoholic  exhilaration,  which  demand  exposure  for  the 
good  of  the   young   and  the   unguarded.     There  is  an 
idea,  widely  entertained,  that  the  effect  of  alcohol  as 
seen  in  the  furious,  or  the  insensible  state  of  drunken- 
ness, differs  in  kind  from  the  exhilaration  produced  by 
a  single  glass  of  wine.     This  is  not  true.     The  action 
of  alcohol  on  the  nervous  system  is  a  unit:  it  is  dimin- 
ished sensibility,  manifesting  itself  in  exhilaration,  and 
this  is  drunkenness  in  kind,  whatever  the  degree  may 
be;    and  the  exhilaration  itself  disqualifies  the  victim 
of  it  from  judging   of  the   degree.      Hence,  it  follows 
that  a  man  who  has  taken  alcohol,  and  is  under  its 
influence,  is  drunk  to  that  extent,  but  how  much  he  is 
drunk  he  is  not  competent  to  know. 

377.  The  Danger  of  the  Poison.— This  last  fact  is 
a    significant    one,     and    solves    the     most     profound 
social  mystery  of   the  past  ages  as  well  as  of  the  pres- 
ent.     It  is  this:    Young  men  see  the  ruin  of  health, 
morals,  fortune,  character,  and  domestic  happiness  in 
the  hundreds  of  their  acquaintances,  who   go  down  to 
early  and  dishonored  graves,  victims  of  the  drinking 


BKAIN   POISONS.  257 

habits  of  society,  and  yet  they  venture  to  travel  the 
same  dangerous  road,  when  one  of  positive  safety  is 
open  to  their  choice. 

They  do  not  understand  that  the  danger  lies  in  tak- 
ing the  poison,  but  suppose  that  it  is  in  taking  too 
much — an  evil  which  they  resolve  always  to  avoid. 
But  not  understanding  the  nature  of  alcohol,  nor 
knowing  that  to  indulge  in  its  exhilaration  is,  to  that 
extent,  to  surrender  the  means  of  self-knowledge,  and 
consequently  of  self-control,  they  move  steadily  on  to 
ruin.  A  knowledge  of  the  physiological  effect  of  nar- 
cotics, and  correct  habits  of  life  established  on  that 
basis,  are  the  only  safeguards  against  their  fascina- 
tions. 

378.  The  Moderate  Use  of  Alcohol.— The  habitual 
use  of  alcoholic  drinks,  even  though  the  quantity  in- 
dulged in  does  not  produce  such  drunkenness  as  will  dis- 
qualify the  subject  for  the  ordinary  business  of  life,  will 
yet  leave  the  unmistakable  traces  of  its  effects  in  a  dis- 
eased condition  of  the  brain  and  nervous  system.  Sensi- 
bility in  all  the  organs  of  the  body  will  be  more  or  less 
blunted;  the  power  to  resist  disease,  and  the  ability  to 
restore  to  healthy  action  the  morbid  condition  of  any 
organ  or  function,  will  be  greatly  impaired,  the  whole 
nutritive  system  will  be  found  the  subject  of  more  or 
less  derangement,  and  the  force  and  endurance  in  the 
muscular  system  will'  feel  the  effect  of  the  poison  in  a 
great  diminution  of  its  energy.  Taken  in  this  manner, 
it  is  a  slow  but  very  sure  poison. 

Recapitulation. 

Narcotics  render  the  food  less  subject  to  change,  and,  therefore, 
more  difficult  of  digestion.  Alcohol  impairs  sensibility  in  all  the 


258  HYGIENE. 

organs.  The  exhilaration  produced  by  alcohol  is  the  result  of 
diminished  sensibility  in  the  nervous  system.  This  disqualifies 
the  person  to  judge  of  his  condition.  Drunkenness  differs  in 
degree,  but  not  in  kind.  The  moderate  use  of  alcohol  is  a  dan- 
gerous delusion. 


LESSON    XLYII. 

BRAIN    POISONS  —  CONTINUED. 

379.  Effects  of  Alcohol  on  the  Mind.— The  effects 
of  alcoholic  drinks  011  the  mental  powers  are  among  the 
most  ruinous,  as  they  are   the  most   prominent  of  its 
morbid   influences.     Exhilaration  is  disturbed  equilib- 
rium of  nervous  force,    with   a   constantly   progressing 
diminution  of  the   aggregate  of  that  force,   ending   in 
insensibility  and  delirium,  and,  finally,  in  unconscious- 
ness. 

While  the  powers  of  imagination  are  momentarily 
exalted,  and  the  command  of  language  is  greater,  the 
judgment  is  impaired,  the  power  of  perception  is  blunt- 
ed, and  the  reasoning  faculties  are  rendered  unreliable. 
With  these  derangements  of  the  purely  intellectual 
faculties,  the  passions  are  excited  to  morbid  activity; 
and  especially  those  of  the  grosser  kind,  being  released 
from  the  restraint  of  the  intellectual  faculties  and 
moral  sensibilities,  lead  their  victim  into  every  species 
of  debauchery  and  crime. 

380.  Alcohol  destroys  Mental  Harmony. —  In  the 

human  constitution,   the   intellectual   powers,  the  ani- 
mal  appetites,   the   passions,   and   the  moral  affections 


ERA IX  POISONS.  259 

are  so  adjusted  that  when  a  healthy  balance  of  power 
is  maintained  among  them,  and  a  proper  subordination 
observed,  the  result  is  the  harmony  pf  the  whole  group, 
bringing  the  highest  happiness  to  the  individual  and 
the  greatest  good  to  society. 

The  universal  testimony  of  all  ages,  and  every  form 
of  civilization,  is,  that  the  use  of  alcohol  has  every- 
where disturbed  this  nicely  adjusted  balance,  and  de- 
stroyed the  equilibrium  among  these  powers,  bringing 
ruin  on  society,  destruction  on  nations,  and  misery  to 
its  immediate  victims,  and  to  the  domestic  circle  in 
which  they  moved.  These  disastrous  results  attract 
attention  most  where  the  poison  is  used  in  large  quan- 
tities, but  the  effect  is  the  same  in  kind,  and  is  always 
in  proportion  to  the  quantity  taken,  other  things  being 
equal. 

381.  Effects  of  Brain-poisoning.  —  The  immediate 
effects  of  alcohol  are  temporary,  and  if  the  quantity 
taken  be  not  very  large,  the  disturbances  pass  off  as 
soon  as  the  alcohol  can  be  discharged  from  the  circula- 
tion by  the  lungs  and  other  organs,  and  the  nerves 
recover  from  its  paralyzing  influence.  Fortunately, 
the  poison  is  volatile,  and  its  vapor  passes  through 
the  membranes  and  other  tissues  of  the  body  with 
scarcely  any  obstruction.  From  this  cause,  death 
seldom  results  immediately  from  alcoholic  poisoning; 
but  the  secondary  effects  of  the  poison  remain  in  a 
train  of  deranged  physical  functions  and  impaired  or 
disturbed  mental  powers. 

The  effect  of  alcohol  on  albumen  is  to  coagulate  it. 
Now,  the  brain  consists  largely  of  albumen,  and  alcohol 
acts  on  it  as  it  does  on  the  white  of  an  egg,  which  is 


260  HYGIENE. 

nearly  pure  albumen:  it  hardens  it,  and  thus  destroys 
its  delicate  texture,  and  proportionally  impairs  all  its 
functions.  This  effect  has  long  been  observed  in  the 
brains  of  habitual  drunkards. 

382.  Alcohol  invites  Disease. — The  membrane  which 
forms  the  walls  of  the  air-cells  in  the  lungs,  as  well  as 
that  which  makes  the  fine  capillary  tubes  of  the  pul- 
monary circulation,  is   highly  albuminous  in  its  char- 
acter.    The  effect  of  alcohol  is  to  thicken  these  mem- 
branes,  and   thus   interrupt   the   easy   transmission   of 
oxygen  to  the  blood  and  of  carbonic  acid  from  it.     This 
effect   on   the    respiratory   organs    will   usually   relieve 
itself  in   a  few   days,  but   in  the  meantime  the  vital 
force  is  diminished  with  the  reduced  supply  of  oxygen, 
and  the  power  to  resist  disease  is  greatly  impaired. 

From  this  cause,  those  who  use  alcoholic  drinks  are 
more  liable  to  be  attacked  with  epidemic  diseases  than 
those  who  abstain.  If  the  use  of  the  poison  becomes 
habitual,  this  effect,  both  on  the  brain  and  respiratory 
organs,  will  be  rendered  permanent,  and  the  impaired 
health  and  obtuse  intellect  will  be  entailed  on  the 
victim. 

383.  Moral  Effects  of  Brain-poisoning.— The  im- 
pressions left  on  the  mental  and  moral  powers  by  long 
and  frequent  indulgence  in  the  use  of  alcohol  may  be 
resolved  into  two  classes:    first,  those  arising  from  an 
enfeebled  will-power;  and,  second,  those  springing  from 
obtuse  moral  perceptions.     Among  the  first  results  of 
even  moderate  drinking  habits,  we  notice  the  loss  of 
self-control.     If  the  friends  of  the   victim    expostulate 
with  him,   and  bring  to  his  blunted  and  obtuse   sen- 
sibilities  a    perception    of    his    danger,    he    betrays   a 


BKAIN  POISONS.  261 

vacillating  will — an  inability  to  take  a  firm  stand 
and  guide  his  future  course  in  the  path  of  absolute 
sobriety. 

This  inability  of  self-control  gives  rise  to  irregular 
and  fitful  moods  of  life,  and  betrays  a  want  of  confi- 
dence on  the  part  of  the  victim,  in  his  ability  to  carry 
out  any  good  resolve  which  he  may  make.  This  weak- 
ening of  the  will-power  betrays  itself  in  the  persistent 
drinking  habits  of  those  who  are  fully  convinced  of  the 
ruin  on.  which  they  are  surely  drifting,  as  well  as  in 
the  numerous  failures  resulting  from  attempts  at  ref- 
ormation. 

384.  Diminished    Will-power.  —  The   force   of  this 
drinking  habit,  of  which  so  much  has  been  said,  re- 
solves itself  chiefly  into  this  feeble  will-power.     If  we 
diminish  the   ability  to   resist  a  force,   we  do,  practi- 
cally, the  same  thing  as  if  we  had  increased  that  force. 
There   is  little  doubt   but   this   is  merely  a   symptom 
indicating  the  diseased  condition  of  the  brain,  present 
in  the  victim  of  the  poison. 

While  the  unfortunate  man  of  drinking  habits  may 
not  be  able  to  carry  into  action  any  good  resolve,  or 
guide  his  life  to  any  virtuous  end  on  account  of  an 
actually  diseased  condition  of  the  brain,  yet  he  is  mor- 
ally responsible :  his  very  disease  is  a  crime — the  crime 
of  his  youth.  All  either  know  or  should  know  that 
alcohol  is  a  poison,  producing  these  effects,  and  to  use 
it  is  to  incur  the  consequences. 

385.  Blunted  Moral  Sensibility.— Perhaps  the  effect 
of  alcohol  which  is  most  to  be  deplored,  is  that  which 
is    exerted    on    the    moral    sensibilities.      More    than 
half  the  crimes  that  are  committed  in  this  country,  are 


262  HYGIENE. 

either  perpetrated  under  the  immediate  influence  of 
alcoholic  delirium,  or  may  be  traced  directly  to  the 
blunting  and  paralyzing  influence  of  the  criminal's 
drinking  habits. 

The  nice  perceptions  of  right  and  wrong,  and  the 
conscientious  regard  for  the  obligations  of  duty,  are  so 
impaired  that  the  person  who  habitually  takes  the 
poison  can  stoop  to  low  and  dishonorable  acts,  or  even 
to  the  commission  of  crimes,  at  which  his  moral  sensi- 
bilities would  have  revolted  when  free  from  the  degrad- 
ing influence  of  the  poison.  The  social  vices,  such  as 
gambling,  licentiousness,  etc.,  if  not  the  direct  out- 
growth of  the  drinking  habits  of-  society,  are,  at  least, 
fostered  by,  and  associated  with  these  habits. 

386.  How  far  these  Derangements  may  be  Cured. — 

After  these  injuries  are  inflicted  on  the  brain  and  its 
appendages,  the  prospect  of  a  permanent  cure  is  very 
remote.  If  the  patient  be  placed  beyond  the  reach  of 
the  poison,  as  in  an  inebriate  asylum,  or  be  sustained 
by  the  encouraging  council  and  sympathy  of  friends, 
and  especially  if  he  be  kept  constantly  employed,  he 
may,  to  some  extent,  restore  a  healthy  action  to  the 
brain  and  reclaim  its  lost  powers,  but  he  is  never  safe. 
His  impaired  will-power  is  never  restored  to  its  origi- 
nal integrity.  His  only  safety  is  in  keeping  beyond 
the  reach  of  the  poison. 

All  experience  proves  that  it  is  not  safe  for  him  to 
taste  alcohol,  even  as  a  medicine.  Here,  as  in  other 
diseased  conditions,  the  true  policy  is  to  prevent  rather 
than  cure,  and,  fortunately  in  this  case,  certain  preven- 
tion is  within  easy  reach  of  every  one.  It  is  simply  not 
to  drink  alcohol  in  any  form. 


TOBACCO.  263 

Recapitulation. 

Alcohol  deranges  the  whole  mental  machinery,  and  destroys 
harmony  of  action  between  the  mental  and  moral  powers.  Its 
immediate  effects  are  temporary  ;  but,  if  the  habitual  use  of  alco- 
hol be  established,  the  derangement  will  become  permanent. 
The  loss  of  self-control  is  among  the  first  effects  of  drinking 
habits.  Moral  sensibilities  are  impaired  by  the  use  of  alcohol. 
How  far  this  diseased  condition  is  curable. 


LESSOX   XLVIII. 

TOBACCO. 

387.  Tobacco — its  mode  of  Poisoning. — Tobacco  is 
among  the  most  powerful  of  the  narcotic  poisons  which 
the  vegetable  kingdom  affords.  It  differs  from  alcohol, 
however,  in  many  particulars,  which  modify  its  effects 
on  those  who  use  it.  As  alcohol  is  the  active  poison  in 
all  the  various  forms  of  intoxicating  drinks,  so  nicotine 
is  the  exhilarating  agent  in  tobacco,  whether  it  be 
chewed,  smoked,  or  taken  as  snuff.  This  nicotine  is  an 
alkaline  principle,  volatile  at  a  high  heat;  but,  at 
ordinary  temperatures,  it  is  not  converted  into  vapor 
in  any  sensible  quantities,  and,  therefore,  does  not 
penetrate  the  membranes  and  pervade  the  tissues  of 
the  whole  body  as  alcohol  does;  and  on  this  account  its 
narcotic  effects  are  slowly  developed. 

In  addition  to  its  exhilarating  effect,  nicotine  is  di- 
rectly emetic,  even  when  the  poison  is  not  taken  into 
the  stomach,  but  absorbed  by  the  skin.  While  the 
paralyzing  effects  of  alcohol  begin  with  the  .nerves  of 
B.  P.— 23. 


264  HYGIENE. 

sensation,  the  action  of  tobacco  is  primarily  on  the  nerves 
of  motion,  diminishing  the  contractile  force  of  the 
muscles. 

388.  Effect  of  Tobacco  on  Digestion.— From  these 
characteristics,  we   will  be  prepared   to  learn  that   to- 
bacco produces  its  disturbances  among  the  nervous  and 
vital  functions  slowly,  and  often  without  the  cause  of 
these  disturbances  being  suspected. 

We  have  already  alluded  (§  269)  to  the  effect  of  the 
use  of  tobacco  on  the  saliva,  and  its  influence  on  the 
perfect  digestion  of  food,  and  we  have  only  to  add  in 
this  place,  that,  in  common  with  all  narcotics,  tobacco 
has  a  tendency  to  prevent  change  in  the  composition 
of  organic  substances,  although  this  tendency  is  feeble 
compared  with  that  of  alcohol. 

The  proportion  of  the  food  digested  in  the  stomach 
of  those  who  use  tobacco,  compared  with  the  digestive 
action  of  those  who  do  not  use  it,  nor  any  other  nar- 
cotic, is  greatly  in  favor  of  the  latter  class,  other  things 
being  equal. 

389.  Tobacco    diminishes  the  Desire  for  Food. — 

The  specific  effect  of  tobacco  on  the  stomach,  tending 
more  or  less  toward  nausea,  has  the  effect  to  diminish 
the  desire  for  food;  and  though  the  rate  at  which  the 
tissues  are  transformed  is  perceptibly  diminished,  yet 
leanness,  and  sometimes  emaciation,  result  from  the 
•^se  of  tobacco.  Perhaps  it  was  this  peculiar  effect  of 
tobacco  which  first  prompted  its  use  among  savages 
(who  were  subject  to  great  irregularity  in  the  supply 
:}f  food),  that  they  might  endure  starvation  without 
suffering  the  pain  of  hunger. 

The  ultimate  effect  of  tobacco,  however,  is  to  slowly 


TOBACCO.  265 

reduce  the  aggregate  of  the  vital  force,  impairing  first 
the  motor  functions  of  the  nervous  system,  affecting  the 
involuntary  motions  more  directly  than  the  voluntary. 
The  senses  most  seriously  affected  by  the  use  of  this 
poison  are  taste  and  smell,  but  this  is  probably  owing 
to  the  local  action  in  the  method  of  using  it. 

390.  Strength  of  the  Tobacco  Habit.— The  feeling 
of  exhilaration  from  the  use  of  tobacco  is  hardly  percep- 
tible until  its  action  is  withdrawn,  when  a  sense  of 
irritability  and  indescribable   wretchedness  takes  pos- 
session of  the  victim  of  the  poison,  and  will  not  yield 
to  any  terms  till  the  exhilaration  is  restored.     Where 
the  habit  is  of  long  standing,  and  the  quantity  used  is 
large,  the  feeling  of  irritability  on  being  deprived  of  it 
sometimes    amounts   to   actual    insanity   for   the   time 
being. 

The  habit,  from  this  cause,  is  even  more  inveterate 
than  that  of  using  alcoholic  drinks,  and  the  power  of 
voluntary  control  over  the  habit  appears  to  be  as  com-  , 
pletely  paralyzed  by  tobacco  as  by  the  more  powerful 
narcotics.  No  one  is  sensible  of  the  effects  of  tobacco 
on  the  nervous  system  till  he  has  abandoned  the  use  of 
it,  and  so  far  recovered  from  its  effects  as  to  have  lost 
the  desire  for  its  peculiar  exhilaration. 

391.  Effect  of  Tobacco  on  the  Mental  Functions.— 

Tobacco  exerts  its  characteristic  influence  on  the  in- 
tellectual functions.  Its  action  is  slow,  and  its  ex- 
hilaration at  any  time  almost  imperceptible;  but  in  a 
series  of  years  it  works  most  disastrous  consequences, 
impairing  first  the  power  of  decision — the  will-power; 
after  that,  the  memory  feels  its  effects,  the  finer  moral 
feelings  are  blunted,  and  the  mental  perceptions  —  the 


266  HYGIENE. 

powers  of  abstract  thought  —  are  impaired,  and  the 
whole  mental  fabric,  slowly  undermined,  falls  into 
ruin. 

So  stealthy  is  its  approach,  so  insidious  its  march, 
that  neither  the  victim  nor  his  friends  suspect  the 
cause  of  his  feeble  health  and  failing  mind;  and 
even  when  the  faithful  physician  has  the  sagacity  to 
detect  the  cause,  and  professional  honor  enough  to  tell 
the  whole  truth  without  concealment,  the  chances  are 
greatly  against  the  patient's  being  able  to  exercise  self- 
control  enough  to  apply  the  proper  remedy  —  the  entire 
disuse  of  the  poison  in  every  form. 

392.  Duration  of  human  Life  aifected  by  Tobacco.— 

Though  tobacco  is  so  active,  and  so  virulent  a  poison, 
yet  it  is  rarely  the  immediate  and  direct  cause  of 
death ;  and  it  has  even  been  affirmed  by  good  physi- 
ologists that  its  use  has  not  diminished  the  average 
duration  of  human  life.  This  does  not  follow,  however, 
from  the  fact  by  which  it  is  sought  to  be  established. 

If  the  duration  of  human  life  now  is  as  great  as  it 
was  two  hundred  years  ago,  or  before  tobacco  came  into 
general  use,  it  must  be  remembered  that  the  average 
comfort  and  protection  of  man  has  greatly  increased, 
and  his  knowledge  of  the  laws  of  health  and  his  means 
of  controlling  diseases,  have  been  greatly  advanced  in 
that  period;  and  if  human  life  has  not  been  corre- 
spondingly prolonged,  there  must  be  some  counteract- 
ing cause.  May  not  that  cause  be  found  in  the  use  of 
alcohol  and  tobacco? 

393.  Early  Decay,  one  of  the  Eifects  of  Tobacco.— 

Whatever  may  be  the  influence  of  tobacco  on  the 
health  and  vital  force  of  those  who  lead  lives  of  mus- 


TOBACCO.  267 

cular  activity  in  the  open  air,  there  can  be  no  question 
of  its  pernicious  effects  on  persons  of  sedentary  habits, 
and  especially  on  those  devoted  to  mental  pursuits. 

The  victim  of  the  tobacco  poison  makes  an  apology 
for  the  use  of  his  cigar  by  declaring  that  it  gives  force 
and  clearness  to  his  mental  operation,  and  yet  he  does 
not  perceive  that  even  that  apology  is  an  admission  of 
the  fearful  effects  of  the  poison  on  brain  action.  If  a 
man  has  so  reduced  his  brain-power  that*  it  is  necessary 
to  cut  off  the  vital  force  from  the  nervous  extremities, 
in  order  to  supply  the  force  for  efficient  brain  action, 
he  is  certainly  011  the  road  to  mental  imbecility  and 
physical  decrepitude.  There  is  no  doubt  but  that  thou- 
sands destroy  years  of  their  ripest  usefulness,  and  in- 
duce imbecility  and  second  childhood,  by  the  habit  of 
using  tobacco. 

394.  Opium — its  peculiarities  as  a  Poison. — Opium 
has  long  been  used  in  China  and  Japan  as  alcohol  and 
tobacco  are  used  in  Europe  and  America.  Within  the 
last  half  century,  the  use  of  opium  as  an  exhilarant  has 
been  increasing  with  alarming  rapidity  in  this  country. 

It  is  a  narcotic,  less  diffusible  than  alcohol,  but  more 
active  than  tobacco,  in  the  ordinary  modes  of  its  use. 
It  is  equally  as  fascinating  in  its  influence  as  either  of 
those  poisons;  and  the  fact  that  it  may  be  used  for 
years  and  yet  its  use  kept  a  secret,  gives  it  a  power 
that  neither  of  those  can  exert.  Tobacco  and  alcohol 
betray  their  victims,  but  opium  keeps  the  secret  for 
them  till  it  binds  them  so  securely  in  its  fetters  that 
escape  is  almost  impossible.  Safety  is  found  only  in 
firmly  discarding  the  use  of  all  narcotics,  except  when 
absolutely  demanded  in  acute  disease. 


268  HYGIENE. 

Recapitulation. 

Tobacco  is  a  less  volatile  poison  than  alcohol.  Its  effect  on  the 
saliva  impairs  digestion,  and  the  tendency  to  induce  nausea  dim- 
inishes the  desire  for  food.  The  exhilaration  from  tobacco  is 
feebler  than  that  from  alcohol;  but,  when  the  habit  is  formed, 
the  desire  for  it  is  equally  strong.  Tobacco  slowly,  but  very  cer- 
tainly, impairs  all  the  mental  functions  of  the  brain,  and  produces 
early  decay  and  premature  old  age.  Opium,  as  an  exhilarant, 
stands  intermediate  between  alcohol  and  tobacco.  Its  use  is 
more  easily  concealed  than  is  the  use  of  alcohol  or  tobacco. 


LESSON    XLIX. 

BRAIN    EXERCISE   AND   REST. 

395.  Early  failure  of  Mental  Faculties.— The  brain, 
as  the  instrument  of  thought,  acquires  power  and  tact 
by  exercise  and  judicious  use.  This  aptitude  is  much 
more  readily  acquired  when  the  brain  action  is  regu- 
lar and  habitual.  Persons  who  have  accustomed  them- 
selves to  exercise  the  mind  in  thought  under  certain 
circumstances,  or  in  connection  with  certain  movements 
of  the  body,  will  find  it  very  difficult  to  bring  all  their 
mental  powers  to  bear  under  different  circumstances. 

The  duration  of  mental  activity,  or  the  period  of  life 
when  mental  force  begins  to  fail,  is  a  subject  which  is 
attracting  much  attention,  both  on  account  of  its  in- 
trinsic importance,  and  because  that  in  different  per- 
sons this  decrepitude  of  old  age  appears  at  periods  so 
widely  different.  Much  of  this  may  depend  on  hered- 
itary constitutional  peculiarities,  but  more  will  be  found 
to  be  connected  with  the  modes  of  mental  training. 


BRAIN   EXERCISE  AND  REST.  269 

Minds  not  trained  to  think  soon  fall  into  decay;  and 
those  in  which  the  training  has  been  confined  to  a  few 
faculties,  and  in  which  all  the  others  have  been  neg- 
lected, fail  early  in  life.  A  broad  and  general  training 
of  all  the  faculties,  and  the  uniform  exercise  of  them, 
will  secure  the  greatest  exemption  from  the  mental 
infirmities  of  age,  other  things  being  equal. 

396.  Brain  rest  —  its  necessity  in  brain  labor. — 

But  brain  activity  demands  rest,  as  activity  every- 
where in  the  vital  machinery  calls  for  its  period  of 
repose.  The  powers  of  thought  may  be  relieved  some- 
what by  changing  the  mode  of  thought,  and  trans- 
ferring the  mental  activity  to  other  channels;  but 
actual  brain  rest  is  obtained  only  in  sound  sleep. 

The  notion  which  was  so  popular  a  few  years  ago, 
that  students  and  brain-wor*kers  in  general  require 
but  little  sleep,  is  not  only  false  but  most  pernicious 
in  its  consequences  on  the  student  who  reduces  it  to 
practice.  The  romance  of  the  "midnight  lamp"  has 
been  a  very  expensive  luxury,  dimming  many  of  the 
brightest  stars  of  human  genius. 

397.  Sleep  should  be  in  proportion  to  brain  activ- 
ity.—  Sleep  should  be   periodical  and  habitual,  if  we 
would  derive  the  greatest  benefit  from  it  as  a  restorer 
of  wasted  brain  force.     As  activity  naturally  associates 
itself  with   light,   so  the   repose  of  sleep   is  associated 
with  darkness;  and  as  the  day  of  twenty-four  hours  is 
nearly  equally  divided  (taking  the  whole  year  together) 
between  light  and  darkness,  there  is  a  very  suggestive 
hint  as  to  the  proper  proportion  of  time  to  be  devoted 
to  rest.     This  will  depend  very  much,  however,  011  the 
intensity  of  brain  action. 


270  HYGIENE. 

If  the  mind  could  be  trained  to  endure  twelve  con- 
secutive hours  of  labor,  the  succeeding  twelve  hours 
should  be  devoted  to  sleep,  in  order  to  repair  the  waste 
of  such  a  protracted  effort.  But  such  prolonged  activity 
is  possible  in  but  few  persons;  and  even  where  it  is 
possible,  it  is  bad  economy.  With  the  best  trained 
and  disciplined  thinkers,  about  two  hours  of  close  appli- 
cation is  the  extent  of  time  which  can  be  economically 
employed  without  an  interval  of  relaxation. 


*.  Wakef ulness — its  effect  and  its  remedy. — The 

student  whose  life  is  properly  divided  between  activity 
and  rest,  will  find  that  from  eight  to  ten  hours  of  quiet, 
sound  sleep  will  be  sufficient  to  maintain  the  highest 
mental  vigor.  Persons  of  irritable,  nervous  systems 
and  of  studious  habits  often  fail  to  sleep  soundly.  This 
wakefulness  may  be  generally  overcome  by  establishing 
and  rigidly  maintaining  the  habit  of  retiring  and 
rising  at  certain  hours. 

A  firm  mattress,  a  well  ventilated  bedroom,  a  light 
and  early  supper,  and  a  cold  sponge  bath  before  lying 
down,  will  seldom  fail  to  procure  sound  sleep.  The 
habit  of  sleeping  at  intervals  during  the  day,  and 
especially  the  regular  after-dinner  siesta,  greatly  inter- 
feres with  the  sound  and  refreshing  quality  of  the 
night's  repose.  Sleep  can  never  be  refreshing  while 
the  stomach  is  engaged  in  the  business  of  digestion, 
and  for  this  reason  we  should  never  eat  within  two 
hours  of  our  time  of  retiring. 

399.  Light — its  effect  on  brain  activity. — Carefully 
conducted  experiments  have  established  the  principle 
that  sleep  is  more  invigorating  when  the  sleeper  is  in 
the  dark  than  in  sunlight;  and,  conversely,  that  activ- 


BKAIN  EXEECISE  AND  REST.  271 

ity  is  best  sustained  in  sunlight,  either  direct  or  dif- 
fused. These  are  truths  too  intimately  connected  with 
health  to  be  neglected  with  impunity.  Sunshine  exerts 
a  strange  force  on  brain  activity,  augmenting  the  power 
with  which  the  whole  vital  machinery  operates. 

Persons  who  work  in  mines  by  means  of  artificial 
light,  and  those  who  live  in  badly  lighted  apartments, 
soon  show  the  effects  of  this  want  of  sunshine  in  the 
reduced  color  of  the  blood,  the  general  relaxation  of  the 
muscular  system,  and  the  diminished  mental  activity. 

400.  Best  Time  for  Sleep. — In  securing  the  number 
of  hours  of  sleep  which  we  propose,  the  time  of  retir- 
ing should  be  fixed  so  that  sleep  will  not  trespass  on 
the  sunlight  of  the  morning.     One  hour  in  the  morning 
is  worth  more  for  mental  labor  than  two  hours  after  ten 
o'clock  in  the  evening.     To  retire  early  and  rise  at  day- 
light is  the  order  of   nature,  and  they  who  violate  it 
will,  sooner  or  later,  pay  the  penalty.     Late   and  irreg- 
ular hours,  inducing  dreamy  slumber  rather  than  sound% 
sleep,  will  dissipate  brain  force,  and  destroy  both  mental 
vigor  and  physical  health. 

401.  Reduction  of  Yital  Force  in  Sleep.  —  Sound, 
refreshing  sleep  is  a  state  of  absolute   inaction  of  all 
the  voluntary  functions,  and  of  entire  unconsciousness 
with  regard  to  ourselves  or  our  surroundings.     The  in- 
voluntary functions  sympathize  with  this  state  of  rest, 
and  the  force  expended  in  their  performance  is  mate- 
rially  reduced.     The    circulation    becomes   slower,    the 
pulse    softer   and   less   forcible,    and   the    breathing    is 
neither  so  full   nor  so  frequent. 

This  reduction  of  vital  action  during  sleep  brings 
several  important  suggestions.  In  sleep  we  are  more 


272  HYGIENE. 

susceptible  to  the  action  of  external  agencies  which 
tend  to  produce  disease  than  when  awake,  and  there- 
fore we  should  be  careful  to  guard  against  them. 

Sleeping  apartments  should  be  well  supplied  with 
fresh  air,  but  its  introduction  should  be  so  arranged 
that  the  sleeper  will  not  be  in  the  direct  current,  or 
draft.  The  production  of  animal  heat  is  reduced  during 
repose,  and  on  this  account  the  sleeper  should  be  pro- 
tected by  sufficient  covering  to  secure  comfort. 

402.  Procuring  Sleep  by  Medicine.  —  Among  the 
many  errors  with  regard  to  sleep,  none  is  more  mis- 
chievous than  the  habit  of  resorting  to  medicine  to 
relieve  sleeplessness.  Anodynes  and  narcotics  never 
produce  natural,  refreshing  rest;  and  the  disturbance 
in  the  nervous  system,  left  as  the  result  of  the  remedy, 
is  generally  more  injurious  than  the  wakefulness  it  was 
intended  to  relieve. 

The  most  dangerous  effect  to  be  dreaded  in  such  use 
of  medicine,  is  the  necessity  of  repeating  and  even 
increasing  the  dose  till  the  habit  becomes  too  strong 
to  be  broken.  But  it  is  especially  in  behalf  of  infants 
that  we  enter  our  solemn  protest  against  the  whole 
family  of  anodynes,  cordials,  soothing  syrups,  etc.  No 
human  power  of  computation  can  measure  the  mischief 
done  to  helpless  humanity  in  this  way  while  yet  in  the 
cradle. 

Recapitulation. 

The  duration  of  the  period  of  mental  activity  is  dependent  on  a 
variety  of  causes.  Uncultivated  minds  fail  at  an  earlier  period 
than  those  properly  trained.  Sleep  necessary  to  maintain  mental 
vigor.  It  should  be  periodical,  and  reduced  to  a  habit.  Wakeful- 


BKAIN   EXERCISE  AND  REST.  273 

ness — its  remedy.  Sleep  should  be  in  the  night,  and  should  be 
a  state  of  absolute  unconsciousness.  Rest  should  not  be  pro- 
cured by  anodyne  medicines. 


LESSON    L. 

ACCIDENTS   AND    DISEASES. 

403.  Injuries   from   Accident.  —  It   has   been   the 
object  of  these  lessons  to  communicate  such  a  knowl- 
edge of  the  laws  of  life  as  will  put  the  student  in  pos- 
session of  the  means  of  preserving  health  and  vigor 
under  all  ordinary  circumstances.    But  with  our  present 
surroundings  we  are  liable  to  injuries  from  accidents 
and   casualties,    which    no   prudence   or   foresight    can 
avoid;    and  even  diseases  may  attack  us,  that  no  in- 
herent vigor  of  health  or  vital  force  will  be  sufficient 
to  throw  off. 

If,  as  has  been  said,  "good  health  is  not  only  a 
blessing,  but  a  duty,"  it  must  be  admitted  to  be,  some- 
times, a  duty  very  difficult  of  performance.  It  is  im- 
portant, therefore,  that  every  body  should  understand 
something  of  the  management  of  the  minor  accidents 
to  which  mankind  is  subject,  and  how  to  treat  the 
slighter  disturbances  of  health  so  as  to  prevent  them 
from  passing  into  the  more  formidable  types  of  disease. 

404.  Bleeding  from   Wounds.  —  In   a  majority  of 
cases  of  minor  accidents  or  of  threatened  disease,  it  is 
not  so  difficult  to  know  what  should  be  done  as  what 
should  not  be  done.     One  of  the   great  difficulties  in 
these  cases  is  to  manage  the  ignorant  officiousness  of 


274  HYGIENE. 

kind  and  benevolent  persons,  who  often  do  immeas- 
urable mischief  when  prompted  by  the  very  best  of 
motives. 

In  all  cuts  or  wounds  made  by  sharp  instruments,1 
the  first  thing  that  demands  attention  is  the  bleeding. 
If  the  blood  flows  rapidly  and  in  jets,  we  will  under- 
stand that  an  artery  is  injured,  and  our  business  is  to 
make  pressure  on  the  bleeding  vessel  near  the  wound, 
on  the  side  toward  the  heart,  by  the  best  means  that 
we  can  devise.  Having  thus  temporarily  arrested  the 
bleeding,  a  surgeon  should  be  obtained  immediately, 
and  the  artery  secured  by  a  ligature.  If  the  injured 
vessel  be  on  the  scalp,  it  may  be  permanently  closed  by 
continued  pressure. 

405.  Treatment  of  Cuts  by  sharp  instruments. — If, 

however,  the  bleeding  be  in  a  regular,  constant  stream, 
we  may  be  assured'  that  the  blood  is  flowing  from  a 
vein  or  veins.  In  this  case  nothing  more  is  necessary 
than  to  apply  cold  water  freely  until  the  bleeding  has 
abated,  when  the  edges  of  the  wound  should  be  care- 
fully drawn  together  and  secured,  in  actual  contact 
with  each  other,  by  strips  of  adhesive  plaster;  and 
where  the  parts  admit  of  it,  the  dressings  should  be 
supported  by  a  light  bandage,  applied  with  only  a 
moderate  degree  of  tightness.  This  dressing  should  not 
be  removed  for  five  or  six  days,  but  may  be  frequently 
wet  with  cold  water.  All  that  is  necessary  is  that  the 
divided  edges  be  maintained  in  contact,  with  nothing 
between  them,  and  that  the  air  be  carefully  excluded 
from  the  injured  part. 

That    is   a   mischievous    error   which    supposes    that 
salves,   ointments,  and   stimulating   applications   have 


ACCIDENTS  AND  DISEASES.  275 

healing  virtues.  Injuries  of  this  kind  can  be  repaired 
only  by  the  vital  force  producing  new  cells,  and  with 
these  uniting  the  divided  tissues  and  thus  repairing 
the  injury. 

406.  Bruises  and  Burns — how  treated. — In  bruises 
and  lacerated  wounds,  the  exclusion  of  the  air  and  the 
application  of  cold  water,  to  keep  down  excessive  in- 
flammation, together   with   absolute  freedom  from  mo- 
tion in  the  parts,  comprise  all  that  is  necessary  to  be 
done.     After  suppuration  has  commenced,   the   wound 
should  be  frequently  washed  with  tepid  water,  and  the 
parts  supported  by  an  appropriate  bandage. 

In  burns  and  scalds  where  the  cuticle  has  been 
removed,  and  a  large  surface  of  the  true  skin  exposed, 
the  important  matter  is  to  secure  protection  from  the 
air.  This  may  be  done  by  saturating  cotton  batting  or 
some  other  soft  substance  with  glycerine,  or  oil  of  any 
kind  that  is  not  rancid  or  stimulating.  The  object 
is  to  substitute  for  the  cuticle  something  that  will  pro- 
tect the  sentient  extremities  of  the  nerves  from  ex- 
posure, which  is  the  cause  of  the  excruciating  pain  of 
burns. 

407.  The  approach  of  Acute  Diseases. — Fevers,  and 
most  acute  diseases,  are  preceded  by  a  sense  of  languor, 
an   indisposition   to   activity,    and   a  loss   of  appetite. 
Admonished  by  these   symptoms,   the  body   should  be 
sponged  with   tepid  water  so  as  to  thoroughly  relieve 
any  mechanical   obstruction  of  the    perspiratory  pores. 
This  should  be  followed  by  brisk  friction  with  a  fleth- 
brush  or  rough  crash  towel  till  a  glow  of  heat   is  felt 
over  the  surface  of  the  skin. 

Follow  this  with    absolute  quiet,   both   of  body  and 


276  HYGIENE. 

mind,  and  limit  the  food  to  gruel,  beef  tea,  or  thin  por- 
ridge, taking  even  these  only  as  the  appetite  calls  for 
them.  If  twenty-four  hours  of  this  treatment  brings  no 
relief,  your  physician  should  be  consulted.  Avoid  all 
excitants,  stimulants,  or  exhilarants,  and  resist  all  per- 
suasions to  take  solid  food  when  the  appetite  admon- 
ishes you  of  the  inability  of  the  stomach  to  digest  it. 

408.  Diarrhea  and  Habitual  Costiveness. — In  warm 
weather,    it    frequently    occurs    that    the    perspiration 
is  suddenly   checked,  and    the    fluids    thrown    to   the 
internal  surface  produce   a  troublesome  diarrhea.     All 
that  is  necessary  in  this  condition,  in  ordinary  cases,  is 
to  use  the  tepid  bath  and  flesh-brush,  drink  copiously 
of  slippery-elm  water,  or  flaxseed  tea,  and  abstain  from 
solid  food  and  from  all  nostrums  which  promise  to  cure 
bowel  complaints. 

Some  persons  are  much  troubled  with  habitual  con- 
stipation of  the  bowels.  Diet  and  exercise  are  the 
remedies  for  this  troublesome  condition.  Bread  made 
of  unbolted  flour,  with  a  free  use  of  succulent  vege- 
tables and  ripe  fruits,  will  seldom  fail  to  relieve  the 
most  stubborn  case  of  costiveness,  if  the  patient  takes 
sufficient  exercise  in  the  open  air. 

409.  Selection  of  a  Physician. — But  few  duties  de- 
volve on  the  heads  of  families  more  important,  and,  to 
most   persons,   more   difficult,   than  the    selection  of  a 
family  physician.     This  difficulty  is  greatly  increased 
by  the  fact   that   people   in   general,  though  well   edu- 
cated, and  intelligent  on  other  subjects,  know  but  little 
of  the  physiological  laws  underlying  the  whole  subject 
of  health. 

A  physician  should,  first  of  all,  be  possessed  of  a  large 


ACCIDENTS  AND  DISEASES.  277 

endowment  of  common  sense  and  moral  honesty.  To 
these  indispensable  qualities  should  be  added  a  thor- 
ough knowledge  of  medical  science  in  all  its  depart- 
ments, and  a  well-trained  faculty  of  close  observation 
and  patient  investigation  of  the  phenomena  of  health 
and  disease,  as  they  will  be  presented  to  him  in  his 
daily  routine  of  business. 

Firmness  and  decision  are  traits  of  character  which 
will  be  largely  in  demand  in  his  daily  intercourse  with 
the  sick.  The  impudence  of  quackery,  the  ignorant 
officiousness  of  well-meaning  friends,  and  the  vacilla- 
ting indecision  of  the  sick,  demand  that,  for  the  safety 
of  the  patient  and  the  maintenance  of  his  own  good 
name  and  clear  conscience,  the  physician  should  exer- 
cise an  unfaltering  firmness. 

410.  Medicines — their  use  and  abuse. —  Among  the 
most  pernicious  ideas  which  have  possessed  the  public 
mind,  is  the  notion  that  health  may  be  disregarded, 
since  we  have  medicines  to  cure  all  the  diseases  our 
recklessness  may  induce.  Let  the  public  learn  that 
medicine  is  always  an  evil — a  great  evil,  though  it  may 
be  necessary  in  order  to  obviate  a  greater  evil. 

One  of  the  most  unaccountable  traits  in  the  character 
of  modern  society  is  the  propensity  to  swallow  drugs, 
and  to  be  deluded  by  the  boastful  pretensions  of  igno- 
rant venders  of  nostrums,  warranted  to  cure  all  dis- 
eases, restore  shattered  constitutions,  and  be  a  perfect 
substitute  for  a  careful  observance  of  the  laws  of  health. 
The  faithful  physician  has  no  higher  duty  to  perform, 
than  to  properly  inform  the  public  mind  on  this  sub- 
ject and  correct  these  fearful  abuses.  But  this  demands 
a  large  share  of  moral  honesty  and  self-denial,  for  the 


278  HYGIENE. 

ill  health  of  the  country,  which  gives  him  his  business, 
is  largely  the  result  of  this  ignorant  and  indiscriminate 
use  of  medicines. 

411.  Preservation  of  Health  a  Moral  Duty.— There 
is  a  moral  obligation  resting  on  every  one  to  preserve 
and  maintain  the  highest  health  that  is  attainable, 
both  of  body  and  mind.  God  has  created  us  for  the 
discharge  of  important  duties  in  life,  and  the  fulfill- 
ment of  this  Divine  purpose  depends  on  the  health 
that  will  give  us  ability  equal  to  the  task.  Within 
certain  limits,  the  means  of  health  arc  placed  in  our 
own  hands,  and  we  can  not,  ignorantly  or  recklessly, 
disregard  its  conditions  without  incurring  guilt. 

We  have  no  more  right  to  render  our  life  a  failure 
than  we  have  to  commit  suicide.  Moreover,  the  laws 
of  life  and  health  are  Divine  laws,  emanating  from  the 
wisdom  and  benevolence  of  the  Creator,  and  to  violate 
them  is  rebellion  against  his  authority.  Our  own  hap- 
piness, the  greatest  good  of  society,  and  our  regard  for 
the  Divine  authority,  all  conspire  to  demand  of  us  a 
thorough  knowledge  and  faithful  observance  of  the 
LAWS  OF  HEALTH. 

Recapitulation. 

Accidental  injuries  are  unavoidable,  therefore  every  person 
should  have  some  knowledge  of  their  treatment.  Bleeding  from 
an  artery  can  be  arrested  only  by  a  ligature.  Cuts  from  sharp 
instruments  require  simple  dressings.  In  burns  and  scalds  the 
surface  must  be  protected.  The  selection  of  a  physician  is  a 
difficult  and  responsible  task.  Medicines,  though  sometimes 
necessary,  are  always  to  be  regarded  as  evils. 


INDEX. 


B.  P.— 24. 


INDEX. 


Absorbents,  39. 
Abstinence  from  food,  199. 
Abstract  thought,  a  human  pecu- 
liarity, 16. 

Adjustment  of  the  eye,  121. 
Air,  composition  of,  43. 

means  of  purifying  it,  212. 
sources  of  its  impurity,  212. 
Air-cells  in  the  lungs,  42. 
Alcohol,  its  effect  on  respiration, 

250. 

its  chemical  relations, 248. 
effect  on  the  transformation 

of  tissues,  250. 
diminishes    muscular  force, 

251. 
its  influence  on  animal  heat, 

252. 

its  influence  on  mind,  258. 
how  far  its  effects  are  curable, 

262. 

Amylaceous  food,  163. 
Anastomosing  vessels,  39. 
Anatomy  defined,  13. 
Animals,  how  distinguished  from 
vegetables,  9. 


Animal  sub-kingdoms.  10. 

Animal  functions,  14. 

Animal  food,  168. 

Aorta,  34. 

Appetite,  when  safe  to  follow,  184. 

bribing  the,  189. 

Aqueous  humor  of  the  eye,  116, 119. 
Arachnoid  membrane,  87. 
Arm,  the  bones  of,  68. 
Arteries,  their  office,  34. 

how  distributed,  35. 
Articulate  animals,  11. 

language,  79,  82. 
Articulations,  61. 
Arytenoid,  cartilage,  80. 
Atmosphere,  composition  of,  211. 
Auricles,  32. 


B 

Bathing,  222. 

Baths,  plunge  and  shower,  224. 
Beans  as  food,  their  character,  172. 
Beef,  its  food  value,  168. 
Birds,  12. 

Bleeding  from  an  artery,  how  dis- 
tinguisbed,  37. 

how  arrested,  274. 

(281) 


282 


INDEX. 


Blood,  the  means  of  purifying  it,  48. 

its  composition,  53. 

quantity  of,  57. 
Blood  disks,  54. 
Bones,  their  use,  58. 

their  composition,  59. 

mechanism  of,  GO,  74. 

not  sensitive,  61. 

their  hygiene,  228. 

liability  to  distortion,  228. 
Brain,  anatomy  of,  85. 

gray  and  white  matter  in,  87. 

complex  function  of,  90. 

its  connection  with  mental 
functions,  138. 

rest  in  sleep,  145. 

exercise  of,  243. 
Bread,  its  importance  as  food,  178. 

rules  for  making,  178. 
Breathing,  how  performed,  45. 

purpose  of,  46. 

too  frequent,  effect  of,  208. 

imperfect,  effect  on  health, 
209. 

its  direct    connection    with 

life,  210. 
Bronchia,  42. 
Burns,  how  treated,  275. 
Butter,  its  food  value,  166. 


Caecum,  28. 

Capillaries,  35. 

Cardiac  orifice,  24. 

Carpus,  the  bones  of,  69,  70. 

Cartilage,  cricoid,  79. 


Cartilage,  arytenoid,  80. 

thyroid,  79. 
Cells  compose  the  tissues,  55. 

how  formed,  55. 

transformation  of,  57. 
Cerebro-spinal  axis,  85. 
|  Cerebrum  and  cerebellum,  86. 
Cerebrum,  connected  with  thought, 

139. 

Cheese  as  food,  166. 
Chemical  changes,  47. 
Chyle,  30. 
Chyme,  26. 

Circulation  of  the  blood,  31-40. 
Classification  of  bodies,  7. 
Clavicle,  69. 
Clothing,  its  relation  to  health,  224. 

material  of,  225,  226. 
Coccyx,  68. 
Cochlea,  105. 

Coffee  as  a  diet  drink,  158. 
Colon,  28. 

Coma,  how  it  differs  from  sleep,  114. 
Comparative  anatomy  defined,  13. 
Compression  of  the  chest,  207. 
Cooking  food,  175. 
Cranial  arch,  65. 

nerves,  88. 

Cranium,  bones  of,  64. 
Cricoid  cartilage,  79. 
Crystalline  lens,  116,  119. 

D 

Diaphragm,  43,  44. 
Digestion,  how  performed,  25. 
Disease  defined,  151. 


INDEX. 


Draft  of  air,  exposure  to,  221. 
Duodenum,  27. 
Dura  Mater,  86. 


Ear,  external,  101. 

drum  of,  102. 
Ear,  bones  of,  103. 
Eating  between  meals,  192. 
Economy  of  motion,  75. 
Eggs  as  food,  167. 
Epiglottis,  80. 
Ethmoid  bone,  65. 
Eustachian  tube,  102. 
Evaporation,  a  cooling  process,  217. 
Exercise   varies   the    quantity    of 
food,  188. 

rules  for,  237. 

Exhilaration  explained,  255. 
Eye,  the  anatomy  of,  111-117. 


Face,  bones  of  the,  65. 

Femur,  70. 

Fermented  drinks,  158. 

Fermenting  bread,  178. 

Fibula,  70. 

Fishes,  12. 

Flour,  varieties  of,  170. 

adulterations  of,  170. 
Food  classified,  19,  160-104. 

and  drink,  154-159. 

quality  of,  165-174. 

preparation  of,  175-179. 

auxiliary,  180-184. 

quantity,  time  of,  185-195. 


Frontal  bone,  64. 

G 

Ganglions,  84,  129. 
Glands,  48. 

salivary,  21. 

lymphatic,  38. 

oil,  50. 

lachrymal,  113. 
Glottis,  80. 

Growth  and  repair,  52. 
Gymnastic  exercise,  238. 

H 

|  Hand,  bones  of,  69. 
Head,  bones  of  the,  64. 
Hearing,  106-111. 

mechanism  of,  108. 
Heart,   its    anatomy    and    action, 

32-34. 
Heat,  its  source  in  animals,  47. 

means  of  reducing,  220. 
Heat-producing  food,  163. 
Hemispheres  of  the  brain,  85. 
Humerus,  69. 
Hygiene  defined,  149. 


Ileo-colic  valve,  28. 

Ileum,  27. 

Images  on  the  retina,  how  formed, 

120. 

Injuries  from  accidents,  etc.,  273. 
Innominatum,  68. 
Inorganic  bodies,  8. 
Intercostal  muscles,  44. 
Intestinal  canal,  its  anatomy,  26, 29. 


284 


INDEX. 


Involuntary  motions,  128. 
Iris,  115. 


Jejunum,  27. 

Joints,  anatomy  of,  61,  62. 

Jugular  Vein,  202. 

K 

Kidneys,  their  office,  49. 
Knee-pan,  70. 


Labyrinth  of  the  ear,  104. 

Lachrymal  gland,  113. 

Lacteals,  their  function,  27. 

Larynx,  79,  82. 

Life-force,  56. 

Life,  graduated  scale  of,  141. 

Ligaments,  61. 

Light  and  brain  activity,  270. 

Liver,  its  function,  29,  48. 

Lungs,  41,  42. 

Lymphatic  vessels,  38. 

M 

Mammalia,  class  of,  12. 
Man,   compared    with    the  lower 
animals,  15. 

his  mental  superiority,  142. 
Manual  labor  as  exercise,  239. 
Mastication,  19. 

importance  of,  193. 
Meat,  how  to  select  it,  169. 

modes  of  cooking,  175. 


Medulla  Oblongata,  86. 

Mesentery,  27. 

Metatarsus,  71. 

Milk  as  a  diet,  165,  166. 

Mind,  its  effect  on  the  circulation, 

204. 

Moderate  drinking,  257. 
Modulation  of  voice,  82. 
Mollusks,  11. 

Motor  and  sentient  nerves,  91. 
Mouth,  19. 
Muscles,  their  anatomy,  72. 

their  arrangement,  74. 

number  of,  77. 

Muscular  contraction,  its  effect  on 
the  circulation,  202. 

exercise,  its  effect,  232. 
Musical  faculties,  109. 

N 

Nerves,  88-95. 

distribution  of,  92. 

of  special  sense,  91. 
Nervous  system,  83. 

peculiar  to  animals,  10. 
Nervous  terminations,  92. 
Nutrition  of  animals  and  plants,  14. 


Occipital  bone,  65. 

(Esophagus,  23. 

Oil  glands,  49. 

Oils  and  fats  as  food,  164,  180. 

Olfactory  nerve,  89,  91. 

Opium,  a  brain  poison,  267. 


INDEX. 


285 


Optic  nerve,  89,  91. 
Organic  bodies,  7. 

character  of,  8. 
Organs  of  special  senses,  101. 
Ossification,  59. 
Over-heated  rooms,  219. 
Oxygen,  its  office  in  respiration, 
213. 


Pacinian  corpuscles,  93. 
Pancreas,  29. 
Parietal  bones,  64. 
Parotid  glands,  21. 
Patella,  70. 
Pelvis,  bones  of,  68. 
Peritoneum,  25. 
Perspiratory  glands,  49. 
Pharynx,  22. 
Physiology  denned,  13. 

its  relation  to  hygiene,  150. 
Pia  Mater,  86. 
Plexus,  Brachial,  90. 

Lumbar,  90. 

Potato,  ijs  food  value,  173. 
Proteine  food,  161. 
Protozoans,  10. 
Pulse,  36. 

Pupil  of  the  eye,  115. 
Pyloric  orifice,  25. 

Q 

Quadrumana,  15. 
Quality  of  food,  165. 
Quantity  of  food,  185. 


R 

Radiate  animals,  11. 

Radius,  69. 

Reflex  motions,  134. 

Relation  of  mind  to  matter,  247. 

Reptiles,  12. 

Respiration,  organs  of,  41. 

its  mechanism,  44. 

its  use,  46. 

Rest,  its  importance,  241. 
Retina,  115. 
Ribs,  action  of  the,  44. 

anatomy  of,  67. 

their  movements  in  breath- 
ing, 206. 

S 

Saliva,  its  use,  22. 
Salivary  glands,  21. 
Salt  necessary  to  health,  181. 
Scapula,  69. 
Sebaceous  follicles,  49. 
Secretion,  21. 
Semicircular  canals,  104. 
Sensation,  method  of,  94. 

grades  of,  97. 
Sentient  nerves,  91. 
Sesamoid  bones,  71. 
Short-sightedness,  123. 
Skeleton,  58,  63. 
Skin,  its  anatomy,  49. 
Skull,  64. 
Sleep,  143. 

true  brain  rest,  269. 

proper  time  for,  271. 


286 


INDEX. 


Smelling,  sense  of,  98. 

Soda,  its  use  in  cooking,  183. 

Sound,  nature  of,  106. 

transmission  of,  107. 

Sphenoid  bone,  65. 

Spinal  column,  65,  66. 
nerves,  89. 

cord,  special    functions    of, 
133. 

Spine,  curvature  of,  231. 

Spleen,  31. 

Sternum,  68. 

Stomach,  its  anatomy  and  func- 
tion, 29. 

Sublingual  glands,  22. 

Submaxillary  glands,  22. 

Sunlight,  its  influence  on  health, 
235. 

Sympathy  of  the  heart  with  other 
organs,  201. 

Symphysis,  63. 


Tarsus,  bones  of,  71. 
Tea  as  a  diet  drink,  158. 
Tears,  113. 
Teeth,  classification  of,  20. 

rules  for  preserving,  194. 
Temperature  of  the  body  in  health, 

51. 
effect  of  on  the  circulation, 

203. 

Temporal  bones,  64. 
Tendons,  their  form  and  use,  73. 


Thoracic  duct,  30". 

Thorax,  41. 

Thought,  a  human  attribute,  16. 

how  related  to  brain.  138. 
Thyroid  cartilage,  79. 
Tibia,  70. 
Tissues,  17. 
Tobacco,  its  effect  on  saliva,  26. 

its  mode  of  action  on  brain 
functions,  263. 

its  effect  on  digestion,  264. 
Trachea,  42. 
Tricuspid  valves,  33. 
Turbinated  bones,  99. 

IT 
Ulna,  position  of,  69,  70. 

V 

Valves  of  the  heart,  33,  34. 
Veins,  34,  36. 

valves  of  the,  37. 

effect  of  pressure  on,  201. 
Vena  Cava,  35. 
Ventricles,  32. 
Vertebras,  anatomy  of,  66. 
Vertebrate  animals,  12. 
Vision,  117-127. 
Vocal  cords,  80. 
Voice,  pitch  of,  81. 

W 

Warming  apartments,  214. 
Water,  sources  of  impurity  of,  150. 


Y 


SERIES. 


ELEMENTS  OF  NATURA^  PHILOSOPHY, 


By  SIDNEY  A. 


m 


Philosophy  is  the  result  ot  many  years' 
experience  in  teaching  the  science  of  Physios.  The  topics  are  consid- 
ered in  their  logical  order,  methodically  developed,  and  thoroughly 
illustrated  and  enforced,  ^-"  .-•* 

While  due  attention  has  been  given  to  the  recent  progress  in  Physics, 
including  the  latest  methods  and  inventions,  it  has  nfttf  been  forgottei 
that  all  facts  are  equally  frf  'i  to  the  tyro. 

NothiT"  ^f  lave 

cardinal^.  ^^^  pils 

studied  fl  /  -    ., 

54»io  1 1 


The  I  -nd 

a  hand-1  ias 

been  prt 

ence  in  ]  UNIVERSITY  OF  CALIFORNIA  LIBRARY  in 

general  i 

The  kmptesr,  most  legible,  and  bifsinesl-like'^\%  of  capitals  and  small 
;  letters  is  adopted  as  the  standard.  After  Copy  Book  No.  4,  duplicate 
books,  with  copies  of  slightly  diminished  size,  are  provided  for  girls. 

Short  sentences  are  introduced  into  the  lower  numbers,  so  that  pupils 
are  not  required  to  write  through  the  whole  series  before  learning  to 
combine  words  into  sentences. 

The  order  of  arrangement,  and  the  gradation  of  copies,  are  more 
complete  than  in  any  other  books  yet  published. 

fi®~  Liberal  terms  on  first  supplies  for  introduction.  Correspondence 
respectfully  solicited. 

WILSON,  HINKLE  &  CO.,  Publishers, 

CINCINNATI,   OHIO. 


